path: root/python/sip/doc/sipref.txt

=====================================================================
 SIP - A Tool for Generating Python Bindings for C and C++ Libraries
=====================================================================

-----------------
 Reference Guide
-----------------

:Contact:   info@riverbankcomputing.co.uk
:Version:   4.6
:Copyright: Copyright (c) 2007 Riverbank Computing Limited

.. contents::
.. section-numbering::


Introduction
============

This is the reference guide for SIP 4.6.  SIP is a tool for
automatically generating `Python <http://www.python.org>`__ bindings for C and
C++ libraries.  SIP was originally developed in 1998 for
`PyQt <http://www.riverbankcomputing.co.uk/pyqt/>`__ - the Python bindings for
the Qt GUI toolkit - but is suitable for generating bindings for any C or C++
library.

This version of SIP generates bindings for Python v2.3 or later.

There are many other similar tools available.  One of the original such tools
is `SWIG <http://www.swig.org>`__ and, in fact, SIP is so called because it
started out as a small SWIG.  Unlike SWIG, SIP is specifically designed for
bringing together Python and C/C++ and goes to great lengths to make the
integration as tight as possible.

The homepage for SIP is http://www.riverbankcomputing.co.uk/sip/.  Here you
will always find the latest stable version, current development snapshots, and
the latest version of this documentation.


License
-------

SIP is licensed under the same terms as Python itself.  SIP places no
restrictions on the license you may apply to the bindings you create.


Features
--------

SIP, and the bindings it produces, have the following features.

    - bindings are fast to load and minimise memory consumption especially when
      only a small sub-set of a large library is being used

    - automatic conversion between standard Python and C/C++ data types

    - overloading of functions and methods with different argument signatures

    - access to a C++ class's protected methods

    - the ability to define a Python class that is a sub-class of a C++ class,
      including abstract C++ classes

    - Python sub-classes can implement the ``__dtor__(self)`` method which
      will be called from the C++ class's virtual destructor

    - support for ordinary C++ functions, class methods, static class methods,
      virtual class methods and abstract class methods

    - the ability to re-implement C++ virtual and abstract methods in Python

    - support for global and class variables

    - support for global and class operators

    - support for C++ namespaces

    - support for C++ templates

    - support for C++ exceptions and wrapping them as Python exceptions

    - the ability to define mappings between C++ classes and similar Python
      data types that are automatically invoked

    - the ability to automatically exploit any available run time type
      information to ensure that the class of a Python instance object matches
      the class of the corresponding C++ instance

    - full support of the Python global interpreter lock, including the ability
      to specify that a C++ function of method may block, therefore allowing
      the lock to be released and other Python threads to run

    - support for the concept of ownership of a C++ instance (i.e. what part of
      the code is responsible for calling the instance's destructor) and how
      the ownership may change during the execution of an application

    - the ability to generate bindings for a C++ class library that itself is
      built on another C++ class library which also has had bindings generated
      so that the different bindings integrate and share code properly

    - a sophisticated versioning system that allows the full lifetime of a C++
      class library, including any platform specific or optional features, to
      be described in a single set of specification files 

    - the ability to include documentation in the specification files which can
      be extracted and subsequently processed by external tools

    - the ability to include copyright notices and licensing information in the
      specification files that is automatically included in all generated
      source code

    - a build system, written in Python, that you can extend to configure,
      compile and install your own bindings without worrying about platform
      specific issues

    - support for building your extensions using distutils

    - SIP, and the bindings it produces, runs under UNIX, Linux, Windows and
      MacOS/X


SIP Components
--------------

SIP comprises a number of different components.

    - The SIP code generator (``sip`` or ``sip.exe``).  This processes ``.sip``
      specification files and generates C or C++ bindings.  It is covered in
      detail in `Using SIP`_.

    - The SIP header file (``sip.h``).  This contains definitions and data
      structures needed by the generated C and C++ code.

    - The SIP module (``sip.so`` or ``sip.pyd``).  This is a Python extension
      module that is imported automatically by SIP generated bindings and
      provides them with some common utility functions.  See also `Using the
      SIP Module in Applications`_.

    - The SIP build system (``sipconfig.py``).  This is a pure Python module
      that is created when SIP is configured and encapsulates all the necessary
      information about your system including relevant directory names,
      compiler and linker flags, and version numbers.  It also includes several
      Python classes and functions which help you write configuration scripts
      for your own bindings.  It is covered in detail in `The SIP Build
      System`_.

    - The SIP distutils extension (``sipdistutils.py``).  This is a distutils
      extension that can be used to build your extension modules using
      distutils and is an alternative to writing configuration scripts with the
      SIP build system.  This can be as simple as adding your .sip files to the
      list of files needed to build the extension module.  It is covered in
      detail in `Building Your Extension with distutils`_.


Qt Support
----------

SIP has specific support for the creation of bindings based on Trolltech's Qt
toolkit.

The SIP code generator understands the signal/slot type safe callback mechanism
that Qt uses to connect objects together.  This allows applications to define
new Python signals, and allows any Python callable object to be used as a slot.

SIP itself does not require Qt to be installed.


Potential Incompatibilities with Earlier Versions
=================================================

SIP v4.4
--------

    - The ``SIP_BUILD`` C preprocessor symbol has been removed.

    - `sipConvertToCpp()`_, `sipIsSubClassInstance()`_ and the old `Generated
      Type Convertors`_ have been deprecated.  The functions
      `sipCanConvertToInstance()`_, `sipConvertToInstance()`_,
      `sipForceConvertToInstance()`_, `sipConvertFromInstance()`_,
      `sipConvertFromNewInstance()`_, `sipCanConvertToMappedType()`_,
      `sipConvertToMappedType()`_, `sipForceConvertToMappedType()`_ and
      `sipConvertFromMappedType()`_ should be used instead.  Handwritten
      `%ConvertFromTypeCode`_ and `%ConvertToTypeCode`_ now has the
      responsibility for using these to implement the ``Transfer`` and
      ``TransferBack`` annotations.


Installing SIP
==============

Downloading SIP
---------------

You can get the latest release of the SIP source code from
http://www.riverbankcomputing.co.uk/sip/download.php.

SIP is also included with all of the major Linux distributions.  However, it
may be a version or two out of date.

You may also find more up to date pre-compiled binaries on
`SourceForge <http://sourceforge.net/project/showfiles.php?group_id=61057>`_.


Configuring SIP
---------------

After unpacking the source package (either a ``.tar.gz`` or a ``.zip`` file
depending on your platform) you should then check for any ``README`` files
that relate to your platform.

Next you need to configure SIP by executing the ``configure.py`` script.  For
example::

    python configure.py

This assumes that the Python interpreter is on your path.  Something like the
following may be appropriate on Windows::

    c:\python25\python configure.py

If you have multiple versions of Python installed then make sure you use the
interpreter for which you wish SIP to generate bindings for.

The full set of command line options is:

-h       Display a help message.
-a       Export all symbols in any SIP generated module and the SIP module
         itself.  This was the default behaviour of SIP prior to v4.2.
         Normally only a module's inititialisation function is exported.  This
         option is deprecated as the ``ModuleMakefile`` class of `The SIP Build
         System`_ allows this to be specified on a per module basis.
-b dir   The SIP code generator will be installed in the directory ``dir``.
-d dir   The SIP module will be installed in the directory ``dir``.
-e dir   The SIP header file will be installed in the directory ``dir``.
-k       The SIP module will be built as a static library.  This is useful when
         building the SIP module as a Python builtin (see
         `Builtin Modules and Custom Interpreters`_).
-n       The SIP code generator and module will be built as universal binaries
         under MacOS/X.
-p plat  Explicitly specify the platform/compiler to be used by the build
         system, otherwise a platform specific default will be used.  The
         ``-h`` option will display all the supported platform/compilers and
         the default.
-u       The SIP module will be built with debugging symbols.
-v dir   By default ``.sip`` files will be installed in the directory ``dir``.

The configure.py script takes many other options that allows the build system
to be finely tuned.  These are of the form ``name=value`` or ``name+=value``.
The ``-h`` option will display each supported ``name``, although not all are
applicable to all platforms.

The ``name=value`` form means that ``value`` will replace the existing value of
``name``.

The ``name+=value`` form means that ``value`` will be appended to the existing
value of ``name``.

For example, the following will disable support for C++ exceptions (and so
reduce the size of module binaries) when used with GCC::

    python configure.py CXXFLAGS+=-fno-exceptions

A pure Python module called ``sipconfig.py`` is generated by ``configure.py``.
This defines each ``name`` and its corresponding ``value``.  Looking at it will
give you a good idea of how the build system uses the different options.  It is
covered in detail in `The SIP Build System`_.


Configuring SIP Using MinGW
***************************

SIP, and the modules it generates, can be built with MinGW, the Windows port of
GCC.  You must use the ``-p`` command line option to specify the correct
platform.  For example::

    c:\python25\python configure.py -p win32-g++


Configuring SIP Using the Borland C++ Compiler
**********************************************

SIP, and the modules it generates, can be built with the free Borland C++
compiler.  You must use the ``-p`` command line option to specify the correct
platform.  For example::

    c:\python25\python configure.py -p win32-borland

You must also make sure you have a Borland-compatible version of the Python
library.  If you are using the standard Python distribution (built using the
Microsoft compiler) then you must convert the format of the Python library.
For example::

    coff2omf python25.lib python25_bcpp.lib


Building SIP
------------

The next step is to build SIP by running your platform's ``make`` command.  For
example::

    make

The final step is to install SIP by running the following command::

    make install

(Depending on your system you may require root or administrator privileges.)

This will install the various SIP components.


Using SIP
=========

Bindings are generated by the SIP code generator from a number of specification
files, typically with a ``.sip`` extension.  Specification files look very
similar to C and C++ header files, but often with additional information (in
the form of a *directive* or an *annotation*) and code so that the bindings
generated can be finely tuned.


A Simple C++ Example
--------------------

We start with a simple example.  Let's say you have a (fictional) C++ library
that implements a single class called ``Word``.  The class has one constructor
that takes a ``\0`` terminated character string as its single argument.  The
class has one method called ``reverse()`` which takes no arguments and returns
a ``\0`` terminated character string.  The interface to the class is defined in
a header file called ``word.h`` which might look something like this::

    // Define the interface to the word library.

    class Word {
        const char *the_word;

    public:
        Word(const char *w);

        char *reverse() const;
    };

The corresponding SIP specification file would then look something like this::

    // Define the SIP wrapper to the word library.

    %Module word 0

    class Word {

    %TypeHeaderCode
    #include <word.h>
    %End

    public:
        Word(const char *w);

        char *reverse() const;
    };

Obviously a SIP specification file looks very much like a C++ (or C) header
file, but SIP does not include a full C++ parser.  Let's look at the
differences between the two files.

    - The `%Module`_ directive has been added [#]_.  This is used to name the
      Python module that is being created and to give it a *generation* number.
      In this example these are ``word`` and ``0`` respectively.  The
      generation number is effectively the version number of the module.

    - The `%TypeHeaderCode`_ directive has been added.  The text between this
      and the following `%End`_ directive is included literally in the code
      that SIP generates.  Normally it is used, as in this case, to
      ``#include`` the corresponding C++ (or C) header file [#]_.

    - The declaration of the private variable ``this_word`` has been removed.
      SIP does not support access to either private or protected instance
      variables.

If we want to we can now generate the C++ code in the current directory by
running the following command::

    sip -c . word.sip

However, that still leaves us with the task of compiling the generated code and
linking it against all the necessary libraries.  It's much easier to use the
SIP build system to do the whole thing.

Using the SIP build system is simply a matter of writing a small Python script.
In this simple example we will assume that the ``word`` library we are wrapping
and it's header file are installed in standard system locations and will be
found by the compiler and linker without having to specify any additional
flags.  In a more realistic example your Python script may take command line
options, or search a set of directories to deal with different configurations
and installations.

This is the simplest script (conventionally called ``configure.py``)::

    import os
    import sipconfig

    # The name of the SIP build file generated by SIP and used by the build
    # system.
    build_file = "word.sbf"

    # Get the SIP configuration information.
    config = sipconfig.Configuration()

    # Run SIP to generate the code.
    os.system(" ".join([config.sip_bin, "-c", ".", "-b", build_file, "word.sip"]))
    
    # Create the Makefile.
    makefile = sipconfig.SIPModuleMakefile(config, build_file)

    # Add the library we are wrapping.  The name doesn't include any platform
    # specific prefixes or extensions (e.g. the "lib" prefix on UNIX, or the
    # ".dll" extension on Windows).
    makefile.extra_libs = ["word"]

    # Generate the Makefile itself.
    makefile.generate()

Hopefully this script is self-documenting.  The key parts are the
``Configuration`` and ``SIPModuleMakefile`` classes.  The build system contains
other Makefile classes, for example to build programs or to call other
Makefiles in sub-directories.

After running the script (using the Python interpreter the extension module is
being created for) the generated C++ code and ``Makefile`` will be in the
current directory.

To compile and install the extension module, just run the following
commands [#]_::

    make
    make install

That's all there is to it.

See `Building Your Extension with distutils`_ for an example of how to build
this example using distutils.

.. [#] All SIP directives start with a ``%`` as the first non-whitespace
       character of a line.
.. [#] SIP includes many code directives like this.  They differ in where the
       supplied code is placed by SIP in the generated code.
.. [#] On Windows you might run ``nmake`` or ``mingw32-make`` instead.


A Simple C Example
------------------

Let's now look at a very similar example of wrapping a fictional C library::

    /* Define the interface to the word library. */

    struct Word {
        const char *the_word;
    };

    struct Word *create_word(const char *w);
    char *reverse(struct Word *word);

The corresponding SIP specification file would then look something like this::

    /* Define the SIP wrapper to the word library. */

    %CModule word 0

    struct Word {

    %TypeHeaderCode
    #include <word.h>
    %End

        const char *the_word;
    };

    struct Word *create_word(const char *w) /Factory/;
    char *reverse(struct Word *word);

Again, let's look at the differences between the two files.

    - The `%CModule`_ directive has been added.  This has the same syntax as
      the `%Module`_ directive used in the previous example but tells SIP that
      the library being wrapped is implemented in C rather than C++.

    - The `%TypeHeaderCode`_ directive has been added.

    - The Factory_ annotation has been added to the ``create_word()`` function.
      This tells SIP that a newly created structure is being returned and it is
      owned by Python.

The ``configure.py`` build system script described in the previous example can
be used for this example without change.


A More Complex C++ Example
--------------------------

In this last example we will wrap a fictional C++ library that contains a class
that is derived from a Qt class.  This will demonstrate how SIP allows a class
hierarchy to be split across multiple Python extension modules, and will
introduce SIP's versioning system.

The library contains a single C++ class called ``Hello`` which is derived from
Qt's ``QLabel`` class.  It behaves just like ``QLabel`` except that the text
in the label is hard coded to be ``Hello World``.  To make the example more
interesting we'll also say that the library only supports Qt v3.0 and later,
and also includes a function called ``setDefault()`` that is not implemented
in the Windows version of the library.

The ``hello.h`` header file looks something like this::

    // Define the interface to the hello library.

    #include <qlabel.h>
    #include <qwidget.h>
    #include <qstring.h>

    class Hello : public QLabel {
        // This is needed by the Qt Meta-Object Compiler.
        Q_OBJECT

    public:
        Hello(QWidget *parent, const char *name = 0, WFlags f = 0);

    private:
        // Prevent instances from being copied.
        Hello(const Hello &);
        Hello &operator=(const Hello &);
    };

    #if !defined(Q_OS_WIN)
    void setDefault(const QString &def);
    #endif

The corresponding SIP specification file would then look something like this::

    // Define the SIP wrapper to the hello library.

    %Module hello 0

    %Import qt/qtmod.sip

    %If (Qt_3_0_0 -)

    class Hello : QLabel {

    %TypeHeaderCode
    #include <hello.h>
    %End

    public:
        Hello(QWidget *parent /TransferThis/, const char *name = 0, WFlags f = 0);

    private:
        Hello(const Hello &);
    };

    %If (!WS_WIN)
    void setDefault(const QString &def);
    %End

    %End

Again we look at the differences, but we'll skip those that we've looked at in
previous examples.

    - The `%Import`_ directive has been added to specify that we are extending
      the class hierarchy defined in the file ``qt/qtmod.sip``.  This file is
      part of PyQt.  The build system will take care of finding the file's
      exact location.

    - The `%If`_ directive has been added to specify that
      everything [#]_ up to the matching `%End`_ directive only applies to Qt
      v3.0 and later.  ``Qt_3_0_0`` is a *tag* defined in ``qtmod.sip`` [#]_
      using the `%Timeline`_ directive.  `%Timeline`_ is used to define a tag
      for each version of a library's API you are wrapping allowing you to
      maintain all the different versions in a single SIP specification.  The
      build system provides support to ``configure.py`` scripts for working out
      the correct tags to use according to which version of the library is
      actually installed.

    - The ``public`` keyword used in defining the super-classes has been
      removed.  This is not supported by SIP.

    - The TransferThis_ annotation has been added to the first argument
      of the constructor.  It specifies that if the argument is not 0 (i.e. the
      ``Hello`` instance being constructed has a parent) then ownership of the
      instance is transferred from Python to C++.  It is needed because Qt
      maintains objects (i.e. instances derived from the ``QObject`` class) in
      a hierachy.  When an object is destroyed all of its children are also
      automatically destroyed.  It is important, therefore, that the Python
      garbage collector doesn't also try and destroy them.  This is covered in
      more detail in `Ownership of Objects`_.  SIP provides many other
      annotations that can be applied to arguments, functions and classes.
      Multiple annotations are separated by commas.  Annotations may have
      values.

    - The ``=`` operator has been removed.  This operator is not supported by
      SIP.

    - The `%If`_ directive has been added to specify that everything up to the
      matching `%End`_ directive does not apply to Windows.  ``WS_WIN`` is
      another tag defined by PyQt, this time using the `%Platforms`_ directive.
      Tags defined by the `%Platforms`_ directive are mutually exclusive, i.e.
      only one may be valid at a time [#]_.

One question you might have at this point is why bother to define the private
copy constructor when it can never be called from Python?  The answer is to
prevent the automatic generation of a public copy constructor.

We now look at the ``configure.py`` script.  This is a little different to the
script in the previous examples for two related reasons.

Firstly, PyQt includes a pure Python module called ``pyqtconfig`` that extends
the SIP build system for modules, like our example, that build on top of PyQt.
It deals with the details of which version of Qt is being used (i.e. it
determines what the correct tags are) and where it is installed.  This is
called a module's configuration module.

Secondly, we generate a configuration module (called ``helloconfig``) for our
own ``hello`` module.  There is no need to do this, but if there is a chance
that somebody else might want to extend your C++ library then it would make
life easier for them.

Now we have two scripts.  First the ``configure.py`` script::

    import os
    import sipconfig
    import pyqtconfig

    # The name of the SIP build file generated by SIP and used by the build
    # system.
    build_file = "hello.sbf"

    # Get the PyQt configuration information.
    config = pyqtconfig.Configuration()

    # Get the extra SIP flags needed by the imported qt module.  Note that
    # this normally only includes those flags (-x and -t) that relate to SIP's
    # versioning system.
    qt_sip_flags = config.pyqt_qt_sip_flags

    # Run SIP to generate the code.  Note that we tell SIP where to find the qt
    # module's specification files using the -I flag.
    os.system(" ".join([config.sip_bin, "-c", ".", "-b", build_file, "-I", config.pyqt_sip_dir, qt_sip_flags, "hello.sip"]))

    # We are going to install the SIP specification file for this module and
    # its configuration module.
    installs = []

    installs.append(["hello.sip", os.path.join(config.default_sip_dir, "hello")])

    installs.append(["helloconfig.py", config.default_mod_dir])

    # Create the Makefile.  The QtModuleMakefile class provided by the
    # pyqtconfig module takes care of all the extra preprocessor, compiler and
    # linker flags needed by the Qt library.
    makefile = pyqtconfig.QtModuleMakefile(
        configuration=config,
        build_file=build_file,
        installs=installs
    )

    # Add the library we are wrapping.  The name doesn't include any platform
    # specific prefixes or extensions (e.g. the "lib" prefix on UNIX, or the
    # ".dll" extension on Windows).
    makefile.extra_libs = ["hello"]

    # Generate the Makefile itself.
    makefile.generate()

    # Now we create the configuration module.  This is done by merging a Python
    # dictionary (whose values are normally determined dynamically) with a
    # (static) template.
    content = {
        # Publish where the SIP specifications for this module will be
        # installed.
        "hello_sip_dir":    config.default_sip_dir,

        # Publish the set of SIP flags needed by this module.  As these are the
        # same flags needed by the qt module we could leave it out, but this
        # allows us to change the flags at a later date without breaking
        # scripts that import the configuration module.
        "hello_sip_flags":  qt_sip_flags
    }

    # This creates the helloconfig.py module from the helloconfig.py.in
    # template and the dictionary.
    sipconfig.create_config_module("helloconfig.py", "helloconfig.py.in", content)

Next we have the ``helloconfig.py.in`` template script::

    import pyqtconfig

    # These are installation specific values created when Hello was configured.
    # The following line will be replaced when this template is used to create
    # the final configuration module.
    # @SIP_CONFIGURATION@

    class Configuration(pyqtconfig.Configuration):
        """The class that represents Hello configuration values.
        """
        def __init__(self, sub_cfg=None):
            """Initialise an instance of the class.

            sub_cfg is the list of sub-class configurations.  It should be None
            when called normally.
            """
            # This is all standard code to be copied verbatim except for the
            # name of the module containing the super-class.
            if sub_cfg:
                cfg = sub_cfg
            else:
                cfg = []

            cfg.append(_pkg_config)

            pyqtconfig.Configuration.__init__(self, cfg)

    class HelloModuleMakefile(pyqtconfig.QtModuleMakefile):
        """The Makefile class for modules that %Import hello.
        """
        def finalise(self):
            """Finalise the macros.
            """
            # Make sure our C++ library is linked.
            self.extra_libs.append("hello")

            # Let the super-class do what it needs to.
            pyqtconfig.QtModuleMakefile.finalise(self)

Again, we hope that the scripts are self documenting.

.. [#] Some parts of a SIP specification aren't subject to version control.
.. [#] Actually in ``versions.sip``.  PyQt uses the `%Include`_ directive to
       split the SIP specification for Qt across a large number of separate
       ``.sip`` files.
.. [#] Tags can also be defined by the `%Feature`_ directive.  These tags are
       not mutually exclusive, i.e. any number may be valid at a time.


Ownership of Objects
--------------------

When a C++ instance is wrapped a corresponding Python object is created.  The
Python object behaves as you would expect in regard to garbage collection - it
is garbage collected when its reference count reaches zero.  What then happens
to the corresponding C++ instance?  The obvious answer might be that the
instance's destructor is called.  However the library API may say that when the
instance is passed to a particular function, the library takes ownership of the
instance, i.e. responsibility for calling the instance's destructor is
transferred from the SIP generated module to the library.

Ownership of an instance may also be associated with another instance.  The
implication being that the owned instance will automatically be destroyed if
the owning instance is destroyed.  SIP keeps track of these relationships to
ensure that Python's cyclic garbage collector can detect and break any
reference cycles between the owning and owned instances.  The association is
implemented as the owning instance taking a reference to the owned instance.

The TransferThis_, Transfer_ and TransferBack annotations are used to specify
where, and it what direction, transfers of ownership happen.  It is very
important that these are specified correctly to avoid crashes (where both
Python and C++ call the destructor) and memory leaks (where neither Python and
C++ call the destructor).

This applies equally to C structures where the structure is returned to the
heap using the ``free()`` function.

See also `sipTransferTo()`_ and `sipTransferBack()`_.


Support for Wide Characters
---------------------------

SIP v4.6 introduced support for wide characters (i.e. the ``wchar_t`` type).
Python's C API includes support for converting between unicode objects and wide
character strings and arrays.  When converting from a unicode object to wide
characters SIP creates the string or array on the heap (using memory allocated
using `sipMalloc()`_).  This then raises the problem of how this memory is
subsequently freed.

The following describes how SIP handles this memory in the different situations
where this is an issue.

    - When a wide string or array is passed to a function or method then the
      memory is freed (using `sipFree()`_) after than function or method
      returns.

    - When a wide string or array is returned from a virtual method then SIP
      does not free the memory until the next time the method is called.

    - When an assignment is made to a wide string or array instance variable
      then SIP does not first free the instance's current string or array.


The Python Global Interpreter Lock
----------------------------------

Python's Global Interpretor Lock (GIL) must be acquired before calls can be
made to the Python API.  It should also be released when a potentially
blocking call to C/C++ library is made in order to allow other Python threads
to be executed.  In addition, some C/C++ libraries may implement their own
locking strategies that conflict with the GIL causing application deadlocks.
SIP provides ways of specifying when the GIL is released and acquired to
ensure that locking problems can be avoided.

SIP always ensures that the GIL is acquired before making calls to the Python
API.  By default SIP does not release the GIL when making calls to the C/C++
library being wrapped.  The ReleaseGIL_ annotation can be used to override
this behaviour when required.

If SIP is given the ``-g`` command line option then the default behaviour is
changed and SIP releases the GIL every time is makes calls to the C/C++
library being wrapped.  The HoldGIL_ annotation can be used to override this
behaviour when required.


The SIP Command Line
====================

The syntax of the SIP command line is::

    sip [options] [specification]

``specification`` is the name of the specification file for the module.  If it
is omitted then ``stdin`` is used.

The full set of command line options is:

-h      Display a help message.
-V      Display the SIP version number.
-a file
        The name of the QScintilla API file to generate.  This file contains a
        description of the module API in a form that the QScintilla editor
        component can use for auto-completion and call tips.  (The file may
        also be used by the SciTE editor but must be sorted first.)  By default
        the file is not generated.
-b file
        The name of the build file to generate.  This file contains the
        information about the module needed by the SIP build system to generate
        a platform and compiler specific Makefile for the module.  By default
        the file is not generated.
-c dir  The name of the directory (which must exist) into which all of the
        generated C or C++ code is placed.  By default no code is generated.
-d file
        The name of the documentation file to generate.  Documentation is
        included in specification files using the `%Doc`_ and `%ExportedDoc`_
        directives.  By default the file is not generated.
-e      Support for C++ exceptions is enabled.  This causes all calls to C++
        code to be enclosed in ``try``/``catch`` blocks and C++ exceptions to
        be converted to Python exceptions.  By default exception support is
        disabled.
-g      The Python GIL is released before making any calls to the C/C++ library
        being wrapped and reacquired afterwards.  See `The Python Global
        Interpreter Lock`_ and the ReleaseGIL_ and HoldGIL_ annotations.
-I dir  The directory is added to the list of directories searched when looking
        for a specification file given in an `%Include`_ or `%Import`_
        directive.  This option may be given any number of times.
-j number
        The generated code is split into the given number of files.  This make
        it easier to use the parallel build facility of most modern
        implementations of ``make``.  By default 1 file is generated for each C
        structure or C++ class.
-r      Debugging statements that trace the execution of the bindings are
        automatically generated.  By default the statements are not generated.
-s suffix
        The suffix to use for generated C or C++ source files.  By default
        ``.c`` is used for C and ``.cpp`` for C++.
-t tag  The SIP version tag (declared using a `%Timeline`_ directive) or the
        SIP platform tag (declared using the `%Platforms`_ directive) to
        generate code for.  This option may be given any number of times so
        long as the tags do not conflict.
-w      The display of warning messages is enabled.  By default warning
        messages are disabled.
-x feature
        The feature (declared using the `%Feature`_ directive) is disabled.
-z file
        The name of a file containing more command line options.


SIP Specification Files
=======================

A SIP specification consists of some C/C++ type and function declarations and
some directives.  The declarations may contain annotations which provide SIP
with additional information that cannot be expressed in C/C++.  SIP does not
include a full C/C++ parser.

It is important to understand that a SIP specification describes the Python
API, i.e. the API available to the Python programmer when they ``import`` the
generated module.  It does not have to accurately represent the underlying
C/C++ library.  There is nothing wrong with omitting functions that make
little sense in a Python context, or adding functions implemented with
handwritten code that have no C/C++ equivalent.  It is even possible (and
sometimes necessary) to specify a different super-class hierarchy for a C++
class.  All that matters is that the generated code compiles properly.

In most cases the Python API matches the C/C++ API.  In some cases handwritten
code (see `%MethodCode`_) is used to map from one to the other without SIP
having to know the details itself.  However, there are a few cases where SIP
generates a thin wrapper around a C++ method or constructor (see `Generated
Derived Classes`_) and needs to know the exact C++ signature.  To deal with
these cases SIP allows two signatures to be specified.  For example::

    class Klass
    {
    public:
        // The Python signature is a tuple, but the underlying C++ signature
        // is a 2 element array.
        Klass(SIP_PYTUPLE) [(int *)];
    %MethodCode
            int iarr[2];

            if (PyArg_ParseTuple(a0, "ii", &iarr[0], &iarr[1]))
            {
                // Note that we use the SIP generated derived class
                // constructor.
                Py_BEGIN_ALLOW_THREADS
                sipCpp = new sipKlass(iarr);
                Py_END_ALLOW_THREADS
            }
    %End
    };


Syntax Definition
-----------------

The following is a semi-formal description of the syntax of a specification
file.

.. parsed-literal::

    *specification* ::= {*module-statement*}

    *module-statement* ::= [*module-directive* | *statement*]

    *module-directive* ::= [`%CModule`_ | `%Copying`_ | `%Doc`_ |
            `%ExportedDoc`_ | `%ExportedHeaderCode`_ | `%Feature`_ |
            `%Import`_ | `%Include`_ | `%License`_ | `%MappedType`_ |
            *mapped-type-template* | `%Module`_ | `%ModuleCode`_ |
            `%ModuleHeaderCode`_ | `%OptionalInclude`_ | `%Platforms`_ |
            `%PreInitialisationCode`_ | `%PostInitialisationCode`_ |
            *sip-option-list* | `%Timeline`_ | `%UnitCode`_]

    *sip-option-list* :: `%SIPOptions`_ ``(`` *option-list* ``)``

    *option-list* ::= *option* [``,`` *option-list*]

    *statement* :: [*class-statement* | *function* | *variable*]

    *class-statement* :: [`%If`_ | *class* | *class-template* | *enum* |
            *namespace* | *opaque-class* | *operator* | *struct* | *typedef* |
            *exception*]

    *class* ::= ``class`` *name* [``:`` *super-classes*] [*class-annotations*]
            ``{`` {*class-line*} ``};``

    *super-classes* ::= *name* [``,`` *super-classes*]

    *class-line* ::= [*class-statement* | `%BIGetReadBufferCode`_ |
            `%BIGetWriteBufferCode`_ | `%BIGetSegCountCode`_ |
            `%BIGetCharBufferCode`_ | `%ConvertToSubClassCode`_ |
            `%ConvertToTypeCode`_ | `%GCClearCode`_ | `%GCTraverseCode`_ |
            `%TypeCode`_ | `%TypeHeaderCode`_ | *constructor* | *destructor* |
            *method* | *static-method* | *virtual-method* | *special-method* |
            *operator* | *virtual-operator* | *class-variable* | ``public:`` |
            ``public slots:`` | ``protected:`` | ``protected slots:`` |
            ``private:`` | ``private slots:`` | ``signals:``]

    *constructor* ::= [``explicit``] *name* ``(`` [*argument-list*] ``)``
            [*exceptions*] [*function-annotations*]
            [*c++-constructor-signature*] ``;`` [`%MethodCode`_]

    *c++-constructor-signature* ::= ``[(`` [*argument-list*] ``)]``

    *destructor* ::= [``virtual``] ``~`` *name* ``()`` [*exceptions*] [``= 0``]
            [*function-annotations*] ``;`` [`%MethodCode`_]
            [`%VirtualCatcherCode`_]

    *method* ::= *type* *name* ``(`` [*argument-list*] ``)`` [``const``]
            [*exceptions*] [``= 0``] [*function-annotations*] [*c++-signature*]
            ``;`` [`%MethodCode`_]

    *c++-signature* ::= ``[`` *type* ``(`` [*argument-list*] ``)]``

    *static-method* ::= ``static`` *function*

    *virtual-method* ::= ``virtual`` *type* *name* ``(`` [*argument-list*] ``)``
            [``const``] [*exceptions*] [``= 0``] [*function-annotations*]
            [*c++-signature*] ``;`` [`%MethodCode`_] [`%VirtualCatcherCode`_]

    *special-method* ::= *type* *special-method-name*
            ``(`` [*argument-list*] ``)`` [*function-annotations*] ``;``
            [`%MethodCode`_]

    *special-method-name* ::= [ ``__abs__`` | ``__add__`` | ``__and__`` |
            ``__call__`` | ``__cmp__`` | ``__contains__`` | ``__delitem__`` |
            ``__div__`` | ``__eq__`` | ``__float__`` | ``__ge__`` |
            ``__getitem__`` | ``__gt__`` | ``__hash__`` | ``__iadd__`` |
            ``__iand__`` | ``__idiv__`` | ``__ilshift__`` | ``__imod__`` |
            ``__imul__`` | ``__int__`` | ``__invert__`` | ``__ior__`` |
            ``__irshift__`` | ``__isub__`` | ``__ixor__`` | ``__le__`` |
            ``__len__`` | ``__long__`` | ``__lshift__`` | ``__lt__`` |
            ``__mod__`` | ``__mul__`` | ``__ne__`` | ``__neg__`` |
            ``__nonzero__`` | ``__or__`` | ``__pos__`` | ``__repr__`` |
            ``__rshift__`` | ``__setitem__`` | ``__str__`` | ``__sub__`` |
            ``__xor__``]

    *operator* ::= *operator-type*
            ``(`` [*argument-list*] ``)`` [``const``] [*exceptions*]
            [*function-annotations*] ``;`` [`%MethodCode`_]

    *virtual-operator* ::= ``virtual`` *operator-type*
            ``(`` [*argument-list*] ``)`` [``const``] [*exceptions*] [``= 0``]
            [*function-annotations*] ``;`` [`%MethodCode`_]
            [`%VirtualCatcherCode`_]

    *operatator-type* ::= [ *operator-function* | *operator-cast* ]

    *operator-function* ::= *type* ``operator`` *operator-name*

    *operator-cast* ::= ``operator`` *type*

    *operator-name* ::= [``+`` | ``-`` | ``*`` | ``/`` | ``%`` | ``&`` |
            ``|`` | ``^`` | ``<<`` | ``>>`` | ``+=`` | ``-=`` | ``*=`` |
            ``/=`` | ``%=`` | ``&=`` | ``|=`` | ``^=`` | ``<<=`` | ``>>=`` |
            ``~`` | ``()`` | ``[]`` | ``<`` | ``<=`` | ``==`` | ``!=`` |
            ``>`` | ``>>=``]

    *class-variable* ::= [``static``] *variable*

    *class-template* :: = ``template`` ``<`` *type-list* ``>`` *class*

    *mapped-type-template* :: = ``template`` ``<`` *type-list* ``>``
            `%MappedType`_

    *enum* ::= ``enum`` [*name*] [*enum-annotations*] ``{`` {*enum-line*} ``};``

    *enum-line* ::= [`%If`_ | *name* [*enum-annotations*] ``,``

    *function* ::= *type* *name* ``(`` [*argument-list*] ``)`` [*exceptions*]
            [*function-annotations*] ``;`` [`%MethodCode`_]

    *namespace* ::= ``namespace`` *name* ``{`` {*namespace-line*} ``};``

    *namespace-line* ::= [`%TypeHeaderCode`_ | *statement*]

    *opaque-class* ::= ``class`` *scoped-name* ``;``

    *struct* ::= ``struct`` *name* ``{`` {*class-line*} ``};``

    *typedef* ::= ``typedef`` [*typed-name* | *function-pointer*] ``;``

    *variable*::= *typed-name* [*variable-annotations*] ``;`` [`%AccessCode`_]
            [`%GetCode`_] [`%SetCode`_]

    *exception* ::= `%Exception`_ *exception-name* [*exception-base*] ``{``
            [`%TypeHeaderCode`_] `%RaiseCode`_ `};``

    *exception-name* ::= *scoped-name*

    *exception-base* ::= ``(`` [*exception-name* | *python-exception*] ``)``

    *python-exception* ::= [``SIP_Exception`` | ``SIP_StopIteration`` |
            ``SIP_StandardError`` | ``SIP_ArithmeticError`` |
            ``SIP_LookupError`` | ``SIP_AssertionError`` |
            ``SIP_AttributeError`` | ``SIP_EOFError`` |
            ``SIP_FloatingPointError`` | ``SIP_EnvironmentError`` |
            ``SIP_IOError`` | ``SIP_OSError`` | ``SIP_ImportError`` |
            ``SIP_IndexError`` | ``SIP_KeyError`` | ``SIP_KeyboardInterrupt`` |
            ``SIP_MemoryError`` | ``SIP_NameError`` | ``SIP_OverflowError`` |
            ``SIP_RuntimeError`` | ``SIP_NotImplementedError`` |
            ``SIP_SyntaxError`` | ``SIP_IndentationError`` | ``SIP_TabError`` |
            ``SIP_ReferenceError`` | ``SIP_SystemError`` | ``SIP_SystemExit`` |
            ``SIP_TypeError`` | ``SIP_UnboundLocalError`` |
            ``SIP_UnicodeError`` | ``SIP_UnicodeEncodeError`` |
            ``SIP_UnicodeDecodeError`` | ``SIP_UnicodeTranslateError`` |
            ``SIP_ValueError`` | ``SIP_ZeroDivisionError`` |
            ``SIP_WindowsError`` | ``SIP_VMSError``]

    *exceptions* ::= ``throw (`` [*exception-list*] ``)``

    *exception-list* ::= *scoped-name* [``,`` *exception-list*]

    *argument-list* ::= *argument* [``,`` *argument-list*] [``,`` ``...``]

    *argument* ::= [*type* [*name*] [*argument-annotations*]
            [*default-value*] | SIP_ANYSLOT_ [*default-value*] | SIP_QOBJECT_ |
            SIP_RXOBJ_CON_ | SIP_RXOBJ_DIS_ | SIP_SIGNAL_ [*default-value*] |
            SIP_SLOT_ [*default-value*] | SIP_SLOT_CON_ | SIP_SLOT_DIS_]

    *default-value* ::= ``=`` *expression*

    *expression* ::= [*value* | *value* *binary-operator* *expression*]

    *value* ::= [*unary-operator*] *simple-value*

    *simple-value* ::= [*scoped-name* | *function-call* | *real-value* |
            *integer-value* | *boolean-value* | *string-value* |
            *character-value*]

    *typed-name*::= *type* *name*

    *function-pointer*::= *type* ``(*`` *name* ``)(`` [*type-list*] ``)``

    *type-list* ::= *type* [``,`` *type-list*]

    *function-call* ::= *scoped-name* ``(`` [*value-list*] ``)``

    *value-list* ::= *value* [``,`` *value-list*]

    *real-value* ::= a floating point number

    *integer-value* ::= a number

    *boolean-value* ::= [``true`` | ``false``]

    *string-value* ::= ``"`` {*character*} ``"``

    *character-value* ::= ````` *character* `````

    *unary-operator* ::= [``!`` | ``~`` | ``-`` | ``+``]

    *binary-operator* ::= [``-`` | ``+`` | ``*`` | ``/`` | ``&`` | ``|``]

    *argument-annotations* ::= see `Argument Annotations`_

    *class-annotations* ::= see `Class Annotations`_

    *enum-annotations* ::= see `Enum Annotations`_

    *function-annotations* ::= see `Function Annotations`_

    *variable-annotations* ::= see `Variable Annotations`_

    *type* ::= [``const``] *base-type* {``*``} [``&``]

    *type-list* ::= *type* [``,`` *type-list*]

    *base-type* ::= [*scoped-name* | *template* | ``struct`` *scoped-name* |
            ``short`` | ``unsigned short`` | ``int`` | ``unsigned`` |
            ``unsigned int`` | ``long`` | ``unsigned long`` | ``float`` |
            ``double`` | ``bool`` | ``char`` | ``signed char`` |
            ``unsigned char`` | ``void`` | ``wchar_t`` | SIP_PYCALLABLE_ |
            SIP_PYDICT_ | SIP_PYLIST_ | SIP_PYOBJECT_ | SIP_PYSLICE_ |
            SIP_PYTUPLE_ | SIP_PYTYPE_]

    *scoped-name* ::= *name* [``::`` *scoped-name*]

    *template* ::= *scoped-name* ``<`` *type-list* ``>``

    *name* ::= _A-Za-z {_A-Za-z0-9}

Here is a short list of differences between C++ and the subset supported by
SIP that might trip you up.

    - SIP does not support the use of ``[]`` in types.  Use pointers instead.

    - A global ``operator`` can only be defined if its first argument is a
      class or a named enum that has been wrapped in the same module.

    - Variables declared outside of a class are effectively read-only.

    - A class's list of super-classes doesn't not include any access specifier
      (e.g. ``public``).


Variable Numbers of Arguments
-----------------------------

SIP supports the use of ``...`` as the last part of a function signature.  Any
remaining arguments are collected as a Python tuple.


Additional SIP Types
--------------------

SIP supports a number of additional data types that can be used in Python
signatures.


SIP_ANYSLOT
***********

This is both a ``const char *`` and a ``PyObject *`` that is used as the type
of the member instead of ``const char *`` in functions that implement the
connection or disconnection of an explicitly generated signal to a slot.
Handwritten code must be provided to interpret the conversion correctly.


SIP_PYCALLABLE
**************

This is a ``PyObject *`` that is a Python callable object.


SIP_PYDICT
**********

This is a ``PyObject *`` that is a Python dictionary object.


SIP_PYLIST
**********

This is a ``PyObject *`` that is a Python list object.


SIP_PYOBJECT
************

This is a ``PyObject *`` of any Python type.


SIP_PYSLICE
***********

This is a ``PyObject *`` that is a Python slice object.


SIP_PYTUPLE
***********

This is a ``PyObject *`` that is a Python tuple object.


SIP_PYTYPE
**********

This is a ``PyObject *`` that is a Python type object.


SIP_QOBJECT
***********

This is a ``QObject *`` that is a C++ instance of a class derived from Qt's
``QObject`` class.


SIP_RXOBJ_CON
*************

This is a ``QObject *`` that is a C++ instance of a class derived from Qt's
``QObject`` class.  It is used as the type of the receiver instead of ``const
QObject *`` in functions that implement a connection to a slot.


SIP_RXOBJ_DIS
*************

This is a ``QObject *`` that is a C++ instance of a class derived from Qt's
``QObject`` class.  It is used as the type of the receiver instead of ``const
QObject *`` in functions that implement a disconnection from a slot.


SIP_SIGNAL
**********

This is a ``const char *`` that is used as the type of the signal instead of
``const char *`` in functions that implement the connection or disconnection
of an explicitly generated signal to a slot.


SIP_SLOT
********

This is a ``const char *`` that is used as the type of the member instead of
``const char *`` in functions that implement the connection or disconnection
of an explicitly generated signal to a slot.


SIP_SLOT_CON
************

This is a ``const char *`` that is used as the type of the member instead of
``const char *`` in functions that implement the connection of an internally
generated signal to a slot.  The type includes a comma separated list of types
that is the C++ signature of of the signal.

To take an example, ``QAccel::connectItem()`` connects an internally generated
signal to a slot.  The signal is emitted when the keyboard accelerator is
activated and it has a single integer argument that is the ID of the
accelerator.  The C++ signature is::

    bool connectItem(int id, const QObject *receiver, const char *member);

The corresponding SIP specification is::

    bool connectItem(int, SIP_RXOBJ_CON, SIP_SLOT_CON(int));


SIP_SLOT_DIS
************

This is a ``const char *`` that is used as the type of the member instead of
``const char *`` in functions that implement the disconnection of an
internally generated signal to a slot.  The type includes a comma separated
list of types that is the C++ signature of of the signal.


SIP Directives
==============

In this section we describe each of the directives that can be used in
specification files.  All directives begin with ``%`` as the first
non-whitespace character in a line.

Some directives have arguments or contain blocks of code or documentation.  In
the following descriptions these are shown in *italics*.  Optional arguments
are enclosed in [*brackets*].

Some directives are used to specify handwritten code.  Handwritten code must
not define names that start with the prefix ``sip``.


%AccessCode
-----------

.. parsed-literal::

    %AccessCode
        *code*
    %End

This directive is used immediately after the declaration of an instance of a
wrapped class or structure, or a pointer to such an instance.  You use it to
provide handwritten code that overrides the default behaviour.

For example::

    class Klass;

    Klass *klassInstance;
    %AccessCode
        // In this contrived example the C++ library we are wrapping defines
        // klassInstance as Klass ** (which SIP doesn't support) so we
        // explicitly dereference it.
        if (klassInstance && *klassInstance)
            return *klassInstance;

        // This will get converted to None.
        return 0;
    %End


%BIGetCharBufferCode
--------------------

.. parsed-literal::

    %BIGetCharBufferCode
        *code*
    %End

This directive (along with `%BIGetReadBufferCode`_, `%BIGetSegCountCode`_ and
`%BIGetWriteBufferCode`_) is used to specify code that implements Python's
buffer interface.  See the section `Buffer Object Structures
<http://www.python.org/dev/doc/devel/api/buffer-structs.html>`__ for the
details.

The following variables are made available to the handwritten code:

*type* \*sipCpp
    This is a pointer to the structure or class instance.  Its *type* is a
    pointer to the structure or class.

void \*\*sipPtrPtr
    This is the pointer used to return the address of the character buffer.

SIP_SSIZE_T sipRes
    The handwritten code should set this to the length of the character buffer
    or -1 if there was an error.

SIP_SSIZE_T sipSegment
    This is the number of the segment of the character buffer.

PyObject \*sipSelf
    This is the Python object that wraps the the structure or class instance,
    i.e. ``self``.


%BIGetReadBufferCode
--------------------

.. parsed-literal::

    %BIGetReadBufferCode
        *code*
    %End

This directive (along with `%BIGetCharBufferCode`_, `%BIGetSegCountCode`_ and
`%BIGetWriteBufferCode`_) is used to specify code that implements Python's
buffer interface.

The following variables are made available to the handwritten code:

*type* \*sipCpp
    This is a pointer to the structure or class instance.  Its *type* is a
    pointer to the structure or class.

void \*\*sipPtrPtr
    This is the pointer used to return the address of the read buffer.

SIP_SSIZE_T sipRes
    The handwritten code should set this to the length of the read buffer or
    -1 if there was an error.

SIP_SSIZE_T sipSegment
    This is the number of the segment of the read buffer.

PyObject \*sipSelf
    This is the Python object that wraps the the structure or class instance,
    i.e. ``self``.


%BIGetSegCountCode
------------------

.. parsed-literal::

    %BIGetSegCountCode
        *code*
    %End

This directive (along with `%BIGetCharBufferCode`_, `%BIGetReadBufferCode`_ and
`%BIGetWriteBufferCode`_) is used to specify code that implements Python's
buffer interface.

The following variables are made available to the handwritten code:

*type* \*sipCpp
    This is a pointer to the structure or class instance.  Its *type* is a
    pointer to the structure or class.

SIP_SSIZE_T \*sipLenPtr
    This is the pointer used to return the total length in bytes of all
    segments of the buffer.

SIP_SSIZE_T sipRes
    The handwritten code should set this to the number of segments that make
    up the buffer.

PyObject \*sipSelf
    This is the Python object that wraps the the structure or class instance,
    i.e. ``self``.


%BIGetWriteBufferCode
---------------------

.. parsed-literal::

    %BIGetWriteBufferCode
        *code*
    %End

This directive (along with `%BIGetCharBufferCode`_, `%BIGetReadBufferCode`_
and `%BIGetSegCountCode`_ is used to specify code that implements Python's
buffer interface.

The following variables are made available to the handwritten code:

*type* \*sipCpp
    This is a pointer to the structure or class instance.  Its *type* is a
    pointer to the structure or class.

void \*\*sipPtrPtr
    This is the pointer used to return the address of the write buffer.

SIP_SSIZE_T sipRes
    The handwritten code should set this to the length of the write buffer or
    -1 if there was an error.

SIP_SSIZE_T sipSegment
    This is the number of the segment of the write buffer.

PyObject \*sipSelf
    This is the Python object that wraps the the structure or class instance,
    i.e. ``self``.


%CModule
--------

.. parsed-literal::

    %CModule *name* [*version*]

This directive is used to identify that the library being wrapped is a C
library and to define the name of the module and it's optional version number.

See the `%Module`_ directive for an explanation of the version number.

For example::

    %CModule dbus 1


%ConvertFromTypeCode
--------------------

.. parsed-literal::

    %ConvertFromTypeCode
        *code*
    %End

This directive is used as part of the `%MappedType`_ directive to specify the
handwritten code that converts an instance of a mapped type to a Python
object.

The following variables are made available to the handwritten code:

*type* \*sipCpp
    This is a pointer to the instance of the mapped type to be converted.  It
    will never be zero as the conversion from zero to ``Py_None`` is handled
    before the handwritten code is called.

PyObject \*sipTransferObj
    This specifies any desired ownership changes to the returned object.  If it
    is ``NULL`` then the ownership should be left unchanged.  If it is
    ``Py_None`` then ownership should be transferred to Python.  Otherwise
    ownership should be transferred to C/C++ and the returned object associated
    with *sipTransferObj*.  The code can choose to interpret these changes in
    any way.  For example, if the code is converting a C++ container of wrapped
    classes to a Python list it is likely that the ownership changes should be
    made to each element of the list.

The handwritten code must explicitly return a ``PyObject *``.  If there was an
error then a Python exception must be raised and ``NULL`` returned.

The following example converts a ``QList<QWidget *>`` instance to a Python
list of ``QWidget`` instances::

    %ConvertFromTypeCode
        PyObject *l;

        // Create the Python list of the correct length.
        if ((l = PyList_New(sipCpp -> size())) == NULL)
            return NULL;

        // Go through each element in the C++ instance and convert it to a
        // wrapped QWidget.
        for (int i = 0; i < sipCpp -> size(); ++i)
        {
            QWidget *w = sipCpp -> at(i);
            PyObject *wobj;

            // Get the Python wrapper for the QWidget instance, creating a new
            // one if necessary, and handle any ownership transfer.
            if ((wobj = sipConvertFromInstance(w, sipClass_QWidget, sipTransferObj)) == NULL)
            {
                // There was an error so garbage collect the Python list.
                Py_DECREF(l);
                return NULL;
            }

            // Add the wrapper to the list.
            PyList_SET_ITEM(l, i, wobj);
        }

        // Return the Python list.
        return l;
    %End


%ConvertToSubClassCode
----------------------

.. parsed-literal::

    %ConvertToSubClassCode
        *code*
    %End

When SIP needs to wrap a C++ class instance it first checks to make sure it
hasn't already done so.  If it has then it just returns a new reference to the
corresponding Python object.  Otherwise it creates a new Python object of the
appropriate type.  In C++ a function may be defined to return an instance of a
certain class, but can often return a sub-class instead.

This directive is used to specify handwritten code that exploits any available
real-time type information (RTTI) to see if there is a more specific Python
type that can be used when wrapping the C++ instance.  The RTTI may be
provided by the compiler or by the C++ instance itself.

The directive is included in the specification of one of the classes that the
handwritten code handles the type conversion for.  It doesn't matter which
one, but a sensible choice would be the one at the root of that class
hierarchy in the module.

Note that if a class hierarchy extends over a number of modules then this
directive should be used in each of those modules to handle the part of the
hierarchy defined in that module.  SIP will ensure that the different pieces
of code are called in the right order to determine the most specific Python
type to use.

The following variables are made available to the handwritten code:

*type* \*sipCpp
    This is a pointer to the C++ class instance.

void \*\*sipCppRet
    When the sub-class is derived from more than one super-class then it is
    possible that the C++ address of the instance as the sub-class is
    different to that of the super-class.  If so, then this must be set to the
    C++ address of the instance when cast (usually using ``static_cast``)
    from the super-class to the sub-class.

sipWrapperType \*sipClass
    The handwritten code must set this to the SIP generated Python type object
    that corresponds to the class instance.  (The type object for class
    ``Klass`` is ``sipClass_Klass``.)  If the RTTI of the class instance isn't
    recognised then ``sipClass`` must be set to ``NULL``.  The code doesn't
    have to recognise the exact class, only the most specific sub-class that
    it can.

The handwritten code must not explicitly return.

The following example shows the sub-class conversion code for ``QEvent`` based
class hierarchy in PyQt::

    class QEvent
    {
    %ConvertToSubClassCode
        // QEvent sub-classes provide a unique type ID.
        switch (sipCpp -> type())
        {
        case QEvent::Timer:
            sipClass = sipClass_QTimerEvent;
            break;

        case QEvent::KeyPress:
        case QEvent::KeyRelease:
            sipClass = sipClass_QKeyEvent;
            break;

        // Skip the remaining event types to keep the example short.

        default:
            // We don't recognise the type.
            sipClass = NULL;
        }
    %End

        // The rest of the class specification.

    };

The SIP API includes the `sipMapIntToClass()`_ and `sipMapStringToClass()`_
functions that convert integer and string based RTTI to Python type objects
based on ordered lookup tables.


%ConvertToTypeCode
------------------

.. parsed-literal::

    %ConvertToTypeCode
        *code*
    %End

This directive is used to specify the handwritten code that converts a Python
object to a mapped type instance and to handle any ownership transfers.  It is
used as part of the `%MappedType`_ directive and as part of a class
specification.  The code is also called to determine if the Python object is of
the correct type prior to conversion.

When used as part of a class specification it can automatically convert
additional types of Python object.  For example, PyQt uses it in the
specification of the ``QString`` class to allow Python string objects and
unicode objects to be used wherever ``QString`` instances are expected.

The following variables are made available to the handwritten code:

int \*sipIsErr
    If this is ``NULL`` then the code is being asked to check the type of the
    Python object.  The check must not have any side effects.  Otherwise the
    code is being asked to convert the Python object and a non-zero value
    should be returned through this pointer if an error occurred during the
    conversion.

PyObject \*sipPy
    This is the Python object to be converted.

*type* \*\*sipCppPtr
    This is a pointer through which the address of the mapped type instance (or
    zero if appropriate) is returned.  Its value is undefined if ``sipIsErr``
    is ``NULL``.

PyObject \*sipTransferObj
    This specifies any desired ownership changes to *sipPy*.  If it is ``NULL``
    then the ownership should be left unchanged.  If it is ``Py_None`` then
    ownership should be transferred to Python.  Otherwise ownership should be
    transferred to C/C++ and *sipPy* associated with *sipTransferObj*.  The
    code can choose to interpret these changes in any way.

The handwritten code must explicitly return an ``int`` the meaning of which
depends on the value of ``sipIsErr``.

If ``sipIsErr`` is ``NULL`` then a non-zero value is returned if the Python
object has a type that can be converted to the mapped type.  Otherwise zero is
returned.

If ``sipIsErr`` is not ``NULL`` then a combination of the following flags is
returned.

        - ``SIP_TEMPORARY`` is set to indicate that the returned instance is a
          temporary and should be released to avoid a memory leak.

        - ``SIP_DERIVED_CLASS`` is set to indicate that the type of the
          returned instance is a derived class.  See `Generated Derived
          Classes`_.

The following example converts a Python list of ``QPoint`` instances to a
``QList<QPoint>`` instance::

    %ConvertToTypeCode
        // See if we are just being asked to check the type of the Python
        // object.
        if (!sipIsErr)
        {
            // Checking whether or not None has been passed instead of a list
            // has already been done.
            if (!PyList_Check(sipPy))
                return 0;

            // Check the type of each element.  We specify SIP_NOT_NONE to
            // disallow None because it is a list of QPoint, not of a pointer
            // to a QPoint, so None isn't appropriate.
            for (int i = 0; i < PyList_GET_SIZE(sipPy); ++i)
                if (!sipCanConvertToInstance(PyList_GET_ITEM(sipPy, i),
                                             sipClass_QPoint, SIP_NOT_NONE))
                    return 0;

            // The type is valid.
            return 1;
        }

        // Create the instance on the heap.
        QList<QPoint> *ql = new QList<QPoint>;

        for (int i = 0; i < PyList_GET_SIZE(sipPy); ++i)
        {
            QPoint *qp;
            int state;

            // Get the address of the element's C++ instance.  Note that, in
            // this case, we don't apply any ownership changes to the list
            // elements, only to the list itself.
            qp = reinterpret_cast<QPoint *>(sipConvertToInstance(
                                                    PyList_GET_ITEM(sipPy, i),
                                                    sipClass_QPoint, 0,
                                                    SIP_NOT_NONE,
                                                    &state, sipIsErr));

            // Deal with any errors.
            if (*sipIsErr)
            {
                sipReleaseInstance(qp, sipClass_QPoint, state);

                // Tidy up.
                delete ql;

                // There is no temporary instance.
                return 0;
            }

            ql -> append(*qp);

            // A copy of the QPoint was appended to the list so we no longer
            // need it.  It may be a temporary instance that should be
            // destroyed, or a wrapped instance that should not be destroyed.
            // sipReleaseInstance() will do the right thing.
            sipReleaseInstance(qp, sipClass_QPoint, state);
        }

        // Return the instance.
        *sipCppPtr = ql;

        // The instance should be regarded as temporary (and be destroyed as
        // soon as it has been used) unless it has been transferred from
        // Python.  sipGetState() is a convenience function that implements
        // this common transfer behaviour.
        return sipGetState(sipTransferObj);
    %End

When used in a class specification the handwritten code replaces the code that
would normally be automatically generated.  This means that the handwritten
code must also handle instances of the class itself and not just the additional
types that are being supported.  This should be done by making calls to
`sipCanConvertToInstance()`_ to check the object type and
`sipConvertToInstance()`_ to convert the object.  The ``SIP_NO_CONVERTORS``
flag *must* be passed to both these functions to prevent recursive calls to the
handwritten code.


%Copying
--------

.. parsed-literal::

    %Copying
        *text*
    %End

This directive is used to specify some arbitrary text that will be included at
the start of all source files generated by SIP.  It is normally used to
include copyright and licensing terms.

For example::

    %Copying
    Copyright (c) 2007 Riverbank Computing Limited
    %End


%Doc
----

.. parsed-literal::

    %Doc
        *text*
    %End

This directive is used to specify some arbitrary text that will be extracted
by SIP when the ``-d`` command line option is used.  The directive can be
specified any number of times and SIP will concatenate all the separate pieces
of text in the order that it sees them.

Documentation that is specified using this directive is local to the module in
which it appears.  It is ignored by modules that `%Import`_ it.  Use the
`%ExportedDoc`_ directive for documentation that should be included by all
modules that `%Import`_ this one.

For example::

    %Doc
    <h1>An Example</h1>
    <p>
    This fragment of documentation is HTML and is local to the module in
    which it is defined.
    </p>
    %End


%End
----

This isn't a directive in itself, but is used to terminate a number of
directives that allow a block of handwritten code or text to be specified.


%Exception
----------

.. parsed-literal::

    %Exception *name* [(*base-exception)]
    {
        [*header-code*]
        *raise-code*
    };

This directive is used to define new Python exceptions, or to provide a stub
for existing Python exceptions.  It allows handwritten code to be provided
that implements the translation between C++ exceptions and Python exceptions.
The arguments to ``throw ()`` specifiers must either be names of classes or the
names of Python exceptions defined by this directive.

*name* is the name of the exception.

*base-exception* is the optional base exception.  This may be either one of
the standard Python exceptions or one defined with a previous `%Exception`_
directive.

*header-code* is the optional `%TypeHeaderCode`_ used to specify any external
interface to the exception being defined.

*raise-code* is the `%RaiseCode`_ used to specify the handwritten code that
converts a reference to the C++ exception to the Python exception.

For example::

    %Exception std::exception(SIP_Exception) /PyName=StdException/
    {
    %TypeHeaderCode
    #include <exception>
    %End
    %RaiseCode
            const char *detail = sipExceptionReference.what();

            SIP_BLOCK_THREADS
            PyErr_SetString(sipException_StdException, detail);
            SIP_UNBLOCK_THREADS
    %End
    };

In this example we map the standard C++ exception to a new Python exception.
The new exception is called ``StdException`` and is derived from the standard
Python exception ``Exception``.


%ExportedDoc
------------

.. parsed-literal::

    %ExportedDoc
        *text*
    %End

This directive is used to specify some arbitrary text that will be extracted
by SIP when the ``-d`` command line option is used.  The directive can be
specified any number of times and SIP will concatenate all the separate pieces
of text in the order that it sees them.

Documentation that is specified using this directive will also be included by
modules that `%Import`_ it.

For example::

    %ExportedDoc
    ==========
    An Example
    ==========
    
    This fragment of documentation is reStructuredText and will appear in the
    module in which it is defined and all modules that %Import it.
    %End


%ExportedHeaderCode
-------------------

.. parsed-literal::

    %ExportedHeaderCode
        *code*
    %End

This directive is used to specify handwritten code, typically the declarations
of types, that is placed in a header file that is included by all generated
code for all modules.  It should not include function declarations because
Python modules should not explicitly call functions in another Python module.

See also `%ModuleCode`_ and `%ModuleHeaderCode`_.


%Feature
--------

.. parsed-literal::

    %Feature *name*

This directive is used to declare a feature.  Features (along with
`%Platforms`_ and `%Timeline`_) are used by the `%If`_ directive to control
whether or not parts of a specification are processed or ignored.

Features are mutually independent of each other - any combination of features
may be enabled or disable.  By default all features are enabled.  The SIP
``-x`` command line option is used to disable a feature.

If a feature is enabled then SIP will automatically generate a corresponding C
preprocessor symbol for use by handwritten code.  The symbol is the name of
the feature prefixed by ``SIP_FEATURE_``.

For example::

    %Feature FOO_SUPPORT

    %If (FOO_SUPPORT)
    void foo();
    %End


%GCClearCode
------------

.. parsed-literal::

    %GCClearCode
        *code*
    %End

Python has a cyclic garbage collector which can identify and release unneeded
objects even when their reference counts are not zero.  If a wrapped C
structure or C++ class keeps its own reference to a Python object then, if the
garbage collector is to do its job, it needs to provide some handwritten code
to traverse and potentially clear those embedded references.

See the section *Supporting cyclic garbage collection* in `Embedding and
Extending the Python Interpreter <http://www.python.org/dev/doc/devel/ext/>`__
for the details.

This directive is used to specify the code that clears any embedded references.
(See `%GCTraverseCode`_ for specifying the code that traverses any embedded
references.)

The following variables are made available to the handwritten code:

*type* \*sipCpp
    This is a pointer to the structure or class instance.  Its *type* is a
    pointer to the structure or class.

int sipRes
    The handwritten code should set this to the result to be returned.

The following simplified example is taken from PyQt.  The ``QCustomEvent``
class allows arbitary data to be attached to the event.  In PyQt this data is
always a Python object and so should be handled by the garbage collector::

    %GCClearCode
        PyObject *obj;

        // Get the object.
        obj = reinterpret_cast<PyObject *>(sipCpp -> data());

        // Clear the pointer.
        sipCpp -> setData(0);

        // Clear the reference.
        Py_XDECREF(obj);

        // Report no error.
        sipRes = 0;
    %End


%GCTraverseCode
---------------

.. parsed-literal::

    %GCTraverseCode
        *code*
    %End

This directive is used to specify the code that traverses any embedded
references for Python's cyclic garbage collector.  (See `%GCClearCode`_ for a
full explanation.)

The following variables are made available to the handwritten code:

*type* \*sipCpp
    This is a pointer to the structure or class instance.  Its *type* is a
    pointer to the structure or class.

visitproc sipVisit
    This is the visit function provided by the garbage collector.

void \*sipArg
    This is the argument to the visit function provided by the garbage
    collector.

int sipRes
    The handwritten code should set this to the result to be returned.

The following simplified example is taken from PyQt's ``QCustomEvent`` class::

    %GCTraverseCode
        PyObject *obj;

        // Get the object.
        obj = reinterpret_cast<PyObject *>(sipCpp -> data());

        // Call the visit function if there was an object.
        if (obj)
            sipRes = sipVisit(obj, sipArg);
        else
            sipRes = 0;
    %End


%GetCode
--------

.. parsed-literal::

    %GetCode
        *code*
    %End

This directive is used after the declaration of a C++ class variable or C
structure member to specify handwritten code to convert it to a Python object.
It is usually used to handle types that SIP cannot deal with automatically.

The following variables are made available to the handwritten code:

*type* \*sipCpp
    This is a pointer to the structure or class instance.  Its *type* is a
    pointer to the structure or class.  It is not made available if the
    variable being wrapped is a static class variable.

PyObject \*sipPy
    The handwritten code must set this to the Python representation of the
    class variable or structure member.  If there is an error then the code
    must raise an exception and set this to ``NULL``.

For example::

    struct Entity
    {
        /*
         * In this contrived example the C library we are wrapping actually
         * defines this as char buffer[100] which SIP cannot handle
         * automatically.
         */
        char *buffer;
    %GetCode
            sipPy = PyString_FromStringAndSize(sipCpp -> buffer, 100);
    %End
    %SetCode
            char *ptr;
            int length;

            if (PyString_AsStringAndSize(sipPy, &ptr, &length) == -1)
                sipErr = 1;
            else if (length != 100)
            {
                /*
                 * Raise an exception because the length isn't exactly right.
                 */

                PyErr_SetString(PyExc_ValueError, "an Entity.buffer must be exactly 100 bytes");
                sipErr = 1;
            }
            else
                memcpy(sipCpp -> buffer, ptr, 100);
    %End
    }


%If
---

.. parsed-literal::

    %If (*expression*)
        *specification*
    %End

where

.. parsed-literal::

    *expression* ::= [*ored-qualifiers* | *range*]

    *ored-qualifiers* ::= [*qualifier* | *qualifier* ``||`` *ored-qualifiers*]

    *qualifier* ::= [``!``] [*feature* | *platform*]

    *range* ::= [*version*] ``-`` [*version*]

This directive is used in conjunction with features (see `%Feature`_),
platforms (see `%Platforms`_) and versions (see `%Timeline`_) to control
whether or not parts of a specification are processed or not.

A *range* of versions means all versions starting with the lower bound up to
but excluding the upper bound.  If the lower bound is omitted then it is
interpreted as being before the earliest version.  If the upper bound is
omitted then it is interpreted as being after the latest version.

For example::

    %Feature SUPPORT_FOO
    %Platforms {WIN32_PLATFORM POSIX_PLATFORM MACOS_PLATFORM}
    %Timeline {V1_0 V1_1 V2_0 V3_0}

    %If (!SUPPORT_FOO)
        // Process this if the SUPPORT_FOO feature is disabled.
    %End

    %If (POSIX_PLATFORM || MACOS_PLATFORM)
        // Process this if either the POSIX_PLATFORM or MACOS_PLATFORM
        // platforms are enabled.
    %End

    %If (V1_0 - V2_0)
        // Process this if either V1_0 or V1_1 is enabled.
    %End

    %If (V2_0 - )
        // Process this if either V2_0 or V3_0 is enabled.
    %End

    %If ( - )
        // Always process this.
    %End

Note that this directive is not implemented as a preprocessor.  Only the
following parts of a specification are affected by it:

    - ``class``
    - `%ConvertFromTypeCode`_
    - `%ConvertToSubClassCode`_
    - `%ConvertToTypeCode`_
    - ``enum``
    - `%ExportedHeaderCode`_
    - functions
    - `%GCClearCode`_
    - `%GCTraverseCode`_
    - `%If`_
    - `%MappedType`_
    - `%MethodCode`_
    - `%ModuleCode`_
    - `%ModuleHeaderCode`_
    - ``namespace``
    - `%PostInitialisationCode`_
    - `%PreInitialisationCode`_
    - ``struct``
    - ``typedef``
    - `%TypeCode`_
    - `%TypeHeaderCode`_
    - `%UnitCode`_
    - variables
    - `%VirtualCatcherCode`_

Also note that the only way to specify the logical and of qualifiers is to use
nested `%If`_ directives.


%Import
-------

.. parsed-literal::

    %Import *filename*

This directive is used to import the specification of another module.  This is
needed if the current module makes use of any types defined in the imported
module, e.g. as an argument to a function, or to sub-class.

If *filename* cannot be opened then SIP prepends *filename* with the name of
the directory containing the current specification file (i.e. the one
containing the `%Import`_ directive) and tries again.  If this also fails then
SIP prepends *filename* with each of the directories, in turn, specified by
the ``-I`` command line option.

For example::

    %Import qt/qtmod.sip


%Include
--------

.. parsed-literal::

    %Include *filename*

This directive is used to include contents of another file as part of the
specification of the current module.  It is the equivalent of the C
preprocessor's ``#include`` directive and is used to structure a large module
specification into manageable pieces.

`%Include`_ follows the same search process as `%Import`_ when trying to open
*filename*.

For example::

    %Include qwidget.sip


%License
--------

.. parsed-literal::

    %License /*license-annotations*/

This directive is used to specify the contents of an optional license
dictionary.  The license dictionary is called ``__license__`` and is stored in
the module dictionary.  The elements of the dictionary are specified using the
Licensee_, Signature_, Timestamp_ and Type_ annotations.  Only the Type_
annotation is compulsory.

Note that this directive isn't an attempt to impose any licensing restrictions
on a module.  It is simply a method for easily embedding licensing information
in a module so that it is accessible to Python scripts.

For example::

    %License /Type="GPL"/


%MappedType
-----------

.. parsed-literal::

    template<*type-list*>
    %MappedType *type*
    {
        [*header-code*]
        [*convert-to-code*]
        [*convert-from-code*]
    };

    %MappedType *type*
    {
        [*header-code*]
        [*convert-to-code*]
        [*convert-from-code*]
    };

This directive is used to define an automatic mapping between a C or C++ type
and a Python type.  It can be used as part of a template, or to map a specific
type.

When used as part of a template *type* cannot itself refer to a template.  Any
occurrences of any of the type names (but not any ``*`` or ``&``) in
*type-list* will be replaced by the actual type names used when the template is
instantiated.  Template mapped types are instantiated automatically as required
(unlike template classes which are only instantiated using ``typedef``).

Any explicit mapped type will be used in preference to any template that maps
the same type, ie. a template will not be automatically instantiated if there
is an explicit mapped type.

*header-code* is the `%TypeHeaderCode`_ used to specify the library interface
to the type being mapped.

*convert-to-code* is the `%ConvertToTypeCode`_ used to specify the handwritten
code that converts a Python object to an instance of the mapped type.

*convert-from-code* is the `%ConvertFromTypeCode`_ used to specify the
handwritten code that converts an instance of the mapped type to a Python
object.

For example::

    template<Type *>
    %MappedType QList
    {
    %TypeHeaderCode
    // Include the library interface to the type being mapped.
    #include <qlist.h>
    %End

    %ConvertToTypeCode
        // See if we are just being asked to check the type of the Python
        // object.
        if (sipIsErr == NULL)
        {
            // Check it is a list.
            if (!PyList_Check(sipPy))
                return 0;

            // Now check each element of the list is of the type we expect.
            // The template is for a pointer type so we don't disallow None.
            for (int i = 0; i < PyList_GET_SIZE(sipPy); ++i)
                if (!sipCanConvertToInstance(PyList_GET_ITEM(sipPy, i),
                                             sipClass_Type, 0))
                    return 0;

            return 1;
        }

        // Create the instance on the heap.
        QList<Type *> *ql = new QList<Type *>;

        for (int i = 0; i < PyList_GET_SIZE(sipPy); ++i)
        {
            // Use the SIP API to convert the Python object to the
            // corresponding C++ instance.  Note that we apply any ownership
            // transfer to the list itself, not the individual elements.
            Type *t = reinterpret_cast<Type *>(sipConvertToInstance(
                                                PyList_GET_ITEM(sipPy, i),
                                                sipClass_Type, 0, 0, 0,
                                                sipIsErr));

            if (*sipIsErr)
            {
                // Tidy up.
                delete ql;

                // There is nothing on the heap.
                return 0;
            }

            // Add the pointer to the C++ instance.
            ql -> append(t);
        }

        // Return the instance on the heap.
        *sipCppPtr = ql;

        // Apply the normal transfer.
        return sipGetState(sipTransferObj);
    %End

    %ConvertFromTypeCode
        PyObject *l;

        // Create the Python list of the correct length.
        if ((l = PyList_New(sipCpp -> size())) == NULL)
            return NULL;

        // Go through each element in the C++ instance and convert it to the
        // corresponding Python object.
        for (int i = 0; i < sipCpp -> size(); ++i)
        {
            Type *t = sipCpp -> at(i);
            PyObject *tobj;

            if ((tobj = sipConvertFromInstance(t, sipClass_Type, sipTransferObj)) == NULL)
            {
                // There was an error so garbage collect the Python list.
                Py_DECREF(l);
                return NULL;
            }

            PyList_SET_ITEM(l, i, tobj);
        }

        // Return the Python list.
        return l;
    %End
    }

Using this we can use, for example, ``QList<QObject *>`` throughout the
module's specification files (and in any module that imports this one).  The
generated code will automatically map this to and from a Python list of QObject
instances when appropriate.


%MethodCode
-----------

.. parsed-literal::

    %MethodCode
        *code*
    %End

This directive is used as part of the specification of a global function, class
method, operator, constructor or destructor to specify handwritten code that
replaces the normally generated call to the function being wrapped.  It is
usually used to handle argument types and results that SIP cannot deal with
automatically.

The specified code is embedded in-line after the function's arguments have
been successfully converted from Python objects to their C or C++ equivalents.
The specified code must not include any ``return`` statements.

In the context of a destructor the specified code is embedded in-line in the
Python type's deallocation function.  Unlike other contexts it supplements
rather than replaces the normally generated code, so it must not include code
to return the C structure or C++ class instance to the heap.  The code is only
called if ownership of the structure or class is with Python.

The specified code must also handle the Python Global Interpreter Lock (GIL).
If compatibility with SIP v3.x is required then the GIL must be released
immediately before the C++ call and reacquired immediately afterwards as shown
in this example fragment::

    Py_BEGIN_ALLOW_THREADS
    sipCpp -> foo();
    Py_END_ALLOW_THREADS

If compatibility with SIP v3.x is not required then this is optional but
should be done if the C++ function might block the current thread or take a
significant amount of time to execute.  (See `The Python Global Interpreter
Lock`_ and the ReleaseGIL_ and HoldGIL_ annotations.)

The following variables are made available to the handwritten code:

*type* a0
    There is a variable for each argument of the Python signature (excluding
    any ``self`` argument) named ``a0``, ``a1``, etc.  The *type* of the
    variable is the same as the type defined in the specification with the
    following exceptions:

    - if the argument is only used to return a value (e.g. it is an ``int *``
      without an In_ annotation) then the type has one less level of
      indirection (e.g. it will be an ``int``)
    - if the argument is a structure or class (or a reference or a pointer to a
      structure or class) then *type* will always be a pointer to the structure
      or class.

    Note that handwritten code for destructors never has any arguments.

PyObject \*a0Wrapper
    This variable is made available only if the corresponding argument wraps a
    C structure or C++ class instance and the GetWrapper_ annotation is
    specified.  The variable is a pointer to the Python object that wraps the
    argument.

*type* \*sipCpp
    If the directive is used in the context of a class constructor then this
    must be set by the handwritten code to the constructed instance.  In any
    other context then this is a pointer to the C structure or C++ class
    instance.  Its *type* is a pointer to the structure or class.

int sipIsErr
    The handwritten code should set this to a non-zero value, and raise an
    appropriate Python exception, if an error is detected.

    ``sipIsErr`` is not provided for destructors.

*type* sipRes
    The handwritten code should set this to the result to be returned.  The
    *type* of the variable is the same as the type defined in the Python
    signature in the specification with the following exception:

    - if the argument is a structure or class (or a reference or a pointer to a
      structure or class) then *type* will always be a pointer to the structure
      or class.

    ``sipRes`` is not provided for inplace operators (e.g. ``+=`` or
    ``__imul__``) as their results are handled automatically, nor for class
    constructors.

PyObject \*sipSelf
    If the directive is used in the context of a class constructor or method
    then this is the Python object that wraps the the structure or class
    instance, i.e. ``self``.

bool sipSelfWasArg
    This is only made available for non-abstract, virtual methods.  It is set
    if ``self`` was explicitly passed as the first argument of the method
    rather than being bound to the method.  In other words, the call was::

        Klass.foo(self, ...)

    rather than::

        self.foo(...)

The following is a complete example::

    class Klass
    {
    public:
        virtual int foo(SIP_PYTUPLE);
    %MethodCode
            // The C++ API takes a 2 element array of integers but passing a
            // two element tuple is more Pythonic.

            int iarr[2];

            if (PyArg_ParseTuple(a0, "ii", &iarr[0], &iarr[1]))
            {
                Py_BEGIN_ALLOW_THREADS
                sipRes = sipSelfWasArg ? sipCpp -> Klass::foo(iarr)
                                       : sipCpp -> foo(iarr);
                Py_END_ALLOW_THREADS
            }
            else
            {
                // PyArg_ParseTuple() will have raised the exception.
                sipIsErr = 1;
            }
    %End
    };

As the example is a virtual method [#]_, note the use of ``sipSelfWasArg`` to
determine exactly which implementation of ``foo()`` to call.

If a method is in the ``protected`` section of a C++ class then the call
should instead be::

    sipRes = sipCpp -> sipProtectVirt_foo(sipSelfWasArg, iarr);

If a method is in the ``protected`` section of a C++ class but is not virtual
then the call should instead be::

    sipRes = sipCpp -> sipProtect_foo(iarr);

.. [#] See `%VirtualCatcherCode`_ for a description of how SIP generated code
       handles the reimplementation of C++ virtual methods in Python.


%Module
-------

.. parsed-literal::

    %Module *name* [*version*]

This directive is used to identify that the library being wrapped is a C++
library and to define the name of the module and it's optional version number.

The name may contain periods to specify that the module is part of a Python
package.

The optional version number is useful if you (or others) might create other
modules that build on this module, i.e. if another module might `%Import`_
this module.  Under the covers, a module exports an API that is used by modules
that `%Import`_ it and the API is given a version number.  A module built on
that module knows the version number of the API that it is expecting.  If,
when the modules are imported at run-time, the version numbers do not match
then a Python exception is raised.  The dependent module must then be re-built
using the correct specification files for the base module.

The version number should be incremented whenever a module is changed.  Some
changes don't affect the exported API, but it is good practice to change the
version number anyway.

For example::

    %Module qt 5


%ModuleCode
-----------

.. parsed-literal::

    %ModuleCode
        *code*
    %End

This directive is used to specify handwritten code, typically the
implementations of utility functions, that can be called by other handwritten
code in the module.

For example::

    %ModuleCode
    // Print an object on stderr for debugging purposes.
    void dump_object(PyObject *o)
    {
        PyObject_Print(o, stderr, 0);
        fprintf(stderr, "\n");
    }
    %End

See also `%ExportedHeaderCode`_ and `%ModuleHeaderCode`_.


%ModuleHeaderCode
-----------------

.. parsed-literal::

    %ModuleHeaderCode
        *code*
    %End

This directive is used to specify handwritten code, typically the declarations
of utility functions, that is placed in a header file that is included by all
generated code for the same module.

For example::

    %ModuleHeaderCode
    void dump_object(PyObject *o);
    %End

See also `%ExportedHeaderCode`_ and `%ModuleCode`_.


%OptionalInclude
----------------

.. parsed-literal::

    %OptionalInclude *filename*

This directive is identical to the `%Include`_ directive except that SIP
silently continues processing if *filename* could not be opened.

For example::

    %OptionalInclude license.sip


%Platforms
----------

.. parsed-literal::

    %Platforms {*name* *name* ...}

This directive is used to declare a set of platforms.  Platforms (along with
`%Feature`_ and `%Timeline`_) are used by the `%If`_ directive to control
whether or not parts of a specification are processed or ignored.

Platforms are mutually exclusive - only one platform can be enabled at a time.
By default all platforms are disabled.  The SIP ``-t`` command line option is
used to enable a platform.

For example::

    %Platforms {WIN32_PLATFORM POSIX_PLATFORM MACOS_PLATFORM}

    %If (WIN32_PLATFORM)
    void undocumented();
    %End

    %If (POSIX_PLATFORM)
    void documented();
    %End


%PostInitialisationCode
-----------------------

.. parsed-literal::

    %PostInitialisationCode
        *code*
    %End

This directive is used to specify handwritten code that is embedded in-line
at the very end of the generated module initialisation code.

The following variables are made available to the handwritten code:

PyObject \*sipModule
    This is the module object returned by ``Py_InitModule()``.

PyObject \*sipModuleDict
    This is the module's dictionary object returned by ``Py_ModuleGetDict()``.

For example::

    %PostInitialisationCode
        // The code will be executed when the module is first imported and
        // after all other initialisation has been completed.
    %End


%PreInitialisationCode
----------------------

.. parsed-literal::

    %PreInitialisationCode
        *code*
    %End

This directive is used to specify handwritten code that is embedded in-line
at the very start of the generated module initialisation code.

For example::

    %PreInitialisationCode
        // The code will be executed when the module is first imported and
        // before other initialisation has been completed.
    %End


%RaiseCode
----------

.. parsed-literal::

    %RaiseCode
        *code*
    %End

This directive is used as part of the definition of an exception using the
`%Exception`_ directive to specify handwritten code that raises a Python
exception when a C++ exception has been caught.  The code is embedded in-line
as the body of a C++ ``catch ()`` clause.

The specified code must handle the Python Global Interpreter Lock (GIL) if
necessary.  The GIL must be acquired before any calls to the Python API and
released after the last call as shown in this example fragment::

    SIP_BLOCK_THREADS
    PyErr_SetNone(PyErr_Exception);
    SIP_UNBLOCK_THREADS

Finally, the specified code must not include any ``return`` statements.

The following variable is made available to the handwritten code:

*type* &sipExceptionRef
    This is a reference to the caught C++ exception.  The *type* of the
    reference is the same as the type defined in the ``throw ()`` specifier.

See the `%Exception`_ directive for an example.


%SetCode
--------

.. parsed-literal::

    %SetCode
        *code*
    %End

This directive is used after the declaration of a C++ class variable or C
structure member to specify handwritten code to convert it from a Python
object.  It is usually used to handle types that SIP cannot deal with
automatically.

The following variables are made available to the handwritten code:

*type* \*sipCpp
    This is a pointer to the structure or class instance.  Its *type* is a
    pointer to the structure or class.  It is not made available if the
    variable being wrapped is a static class variable.

int sipErr
    If the conversion failed then the handwritten code should raise a Python
    exception and set this to a non-zero value.  Its initial value will be
    automatically set to zero.

PyObject \*sipPy
    This is the Python object that the handwritten code should convert.

See the `%GetCode`_ directive for an example.


%SIPOptions
-----------

This directive sets one or more options that controls different aspects of
SIP's behaviour.  In this version all the available options are provided
specifically to support PyQt and so are not documented.


%Timeline
---------

.. parsed-literal::

    %Timeline {*name* *name* ...}

This directive is used to declare a set of versions released over a period of
time.  Versions (along with `%Feature`_ and `%Platforms`_) are used by the
`%If`_ directive to control whether or not parts of a specification are
processed or ignored.

Versions are mutually exclusive - only one version can be enabled at a time.
By default all versions are disabled.  The SIP ``-t`` command line option is
used to enable a version.

For example::

    %Timeline {V1_0 V1_1 V2_0 V3_0}

    %If (V1_0 - V2_0)
    void foo();
    %End

    %If (V2_0 -)
    void foo(int = 0);
    %End

`%Timeline`_ can be used any number of times in a module to allow multiple
libraries to be wrapped in the same module.


%TypeCode
---------

.. parsed-literal::

    %TypeCode
        *code*
    %End

This directive is used as part of the specification of a C structure or a C++
class to specify handwritten code, typically the implementations of utility
functions, that can be called by other handwritten code in the structure or
class.

For example::

    class Klass
    {
    %TypeCode
    // Print an instance on stderr for debugging purposes.
    static void dump_klass(const Klass *k)
    {
        fprintf(stderr,"Klass %s at %p\n", k -> name(), k);
    }
    %End

        // The rest of the class specification.

    };

Because the scope of the code is normally within the generated file that
implements the type, any utility functions would normally be declared
``static``.  However a naming convention should still be adopted to prevent
clashes of function names within a module in case the SIP ``-j`` command line
option is used.


%TypeHeaderCode
---------------

.. parsed-literal::

    %TypeHeaderCode
        *code*
    %End

This directive is used to specify handwritten code that defines the interface
to a C or C++ type being wrapped, either a structure, a class, or a template.
It is used within a class definition or a `%MappedType`_ directive.

Normally *code* will be a pre-processor ``#include`` statement.

For example::

    // Wrap the Klass class.
    class Klass
    {
    %TypeHeaderCode
    #include <klass.h>
    %End

        // The rest of the class specification.
    };


%UnitCode
---------

.. parsed-literal::

    %UnitCode
        *code*
    %End

This directive is used to specify handwritten code that it included at the very
start of a generated compilation unit (ie. C or C++ source file).  It is
typically used to ``#include`` a C++ precompiled header file.


%VirtualCatcherCode
-------------------

.. parsed-literal::

    %VirtualCatcherCode
        *code*
    %End

For most classes there are corresponding `generated derived classes`_ that
contain reimplementations of the class's virtual methods.  These methods (which
SIP calls catchers) determine if there is a corresponding Python
reimplementation and call it if so.  If there is no Python reimplementation
then the method in the original class is called instead.

This directive is used to specify handwritten code that replaces the normally
generated call to the Python reimplementation and the handling of any returned
results.  It is usually used to handle argument types and results that SIP
cannot deal with automatically.

This directive can also be used in the context of a class destructor to
specify handwritten code that is embedded in-line in the internal derived
class's destructor.

In the context of a method the Python Global Interpreter Lock (GIL) is
automatically acquired before the specified code is executed and automatically
released afterwards.

In the context of a destructor the specified code must handle the GIL.  The
GIL must be acquired before any calls to the Python API and released after the
last call as shown in this example fragment::

    SIP_BLOCK_THREADS
    Py_DECREF(obj);
    SIP_UNBLOCK_THREADS

The following variables are made available to the handwritten code in the
context of a method:

*type* a0
    There is a variable for each argument of the C++ signature named ``a0``,
    ``a1``, etc.  The *type* of the variable is the same as the type defined in
    the specification.

int sipIsErr
    The handwritten code should set this to a non-zero value, and raise an
    appropriate Python exception, if an error is detected.

PyObject \*sipMethod
    This object is the Python reimplementation of the virtual C++ method.  It
    is normally passed to `sipCallMethod()`_.

*type* sipRes
    The handwritten code should set this to the result to be returned.  The
    *type* of the variable is the same as the type defined in the C++ signature
    in the specification.

No variables are made available in the context of a destructor.

For example::

    class Klass
    {
    public:
        virtual int foo(SIP_PYTUPLE) [int (int *)];
    %MethodCode
            // The C++ API takes a 2 element array of integers but passing a
            // two element tuple is more Pythonic.

            int iarr[2];

            if (PyArg_ParseTuple(a0, "ii", &iarr[0], &iarr[1]))
            {
                Py_BEGIN_ALLOW_THREADS
                sipRes = sipCpp -> Klass::foo(iarr);
                Py_END_ALLOW_THREADS
            }
            else
            {
                // PyArg_ParseTuple() will have raised the exception.
                sipIsErr = 1;
            }
    %End
    %VirtualCatcherCode
            // Convert the 2 element array of integers to the two element
            // tuple.

            PyObject *result;

            result = sipCallMethod(&sipIsErr, sipMethod, "ii", a0[0], a0[1]);

            if (result != NULL)
            {
                // Convert the result to the C++ type.
                sipParseResult(&sipIsErr, sipMethod, result, "i", &sipRes);

                Py_DECREF(result);
            }
    %End
    };


SIP Annotations
===============

In this section we describe each of the annotations that can be used in
specification files.

Annotations can either be argument annotations, class annotations, enum
annotations, exception annotations, function annotations, license annotations,
or variable annotations depending on the context in which they can be used.

Annotations are placed between forward slashes (``/``).  Multiple annotations
are comma separated within the slashes.

Annotations have a type and, possibly, a value.  The type determines the
format of the value.  The name of an annotation and its value are separated by
``=``.

Annotations can have one of the following types:

boolean
    This type of annotation has no value and is implicitly true.

name
    The value is a name that is compatible with a C/C++ identifier.  In some
    cases the value is optional.

string
    The value is a double quoted string.

The following example shows argument and function annotations::

    void exec(QWidget * /Transfer/) /ReleaseGIL, PyName=call_exec/;

Note that the current version of SIP does not complain about unknown
annotations, or annotations used out of their correct context.


Argument Annotations
--------------------

AllowNone
*********

This boolean annotation specifies that the value of the corresponding argument
(which should be either SIP_PYCALLABLE_, SIP_PYDICT_, SIP_PYLIST_,
SIP_PYSLICE_, SIP_PYTUPLE_ or SIP_PYTYPE_) may be ``None``.


Array
*****

This boolean annotation specifies that the corresponding argument (which
should be either ``char *`` or ``unsigned char *``) refers to an array
rather than a ``'\0'`` terminated string.  There must be a corresponding
argument with the ArraySize_ annotation specified.  The annotation may only be
specified once in a list of arguments.


ArraySize
*********

This boolean annotation specifies that the corresponding argument (which
should be either ``short``, ``unsigned short``, ``int``, ``unsigned``,
``long`` or ``unsigned long``) refers to the size of an array.  There must be
a corresponding argument with the Array_ annotation specified.  The annotation
may only be specified once in a list of arguments.


Constrained
***********

Python will automatically convert between certain compatible types.  For
example, if a floating pointer number is expected and an integer supplied,
then the integer will be converted appropriately.  This can cause problems
when wrapping C or C++ functions with similar signatures.  For example::

    // The wrapper for this function will also accept an integer argument
    // which Python will automatically convert to a floating point number.
    void foo(double);

    // The wrapper for this function will never get used.
    void foo(int);

This boolean annotation specifies that the corresponding argument (which
should be either ``bool``, ``int``, ``float``, ``double`` or a wrapped class)
must match the type without any automatic conversions.  In the context of a
wrapped class the invocation of any `%ConvertToTypeCode`_ is suppressed.

The following example gets around the above problem::

    // The wrapper for this function will only accept floating point numbers.
    void foo(double /Constrained/);

    // The wrapper for this function will be used for anything that Python can
    // convert to an integer, except for floating point numbers.
    void foo(int);


GetWrapper
**********

This boolean annotation is only ever used in conjunction with handwritten code
specified with the `%MethodCode`_ directive.  It causes an extra variable to
be generated for the corresponding argument (which should be a wrapped C
structure or C++ class instance) which is a pointer to the Python object that
wraps the argument.

See the `%MethodCode`_ directive for more detail.


In
**

This boolean annotation is used to specify that the corresponding argument
(which should be a pointer type) is used to pass a value to the function.

For pointers to wrapped C structures or C++ class instances, ``char *`` and
``unsigned char *`` then this annotation is assumed unless the Out_ annotation
is specified.

For pointers to other types then this annotation must be explicitly specified
if required.  The argument will be dereferenced to obtain the actual value.

Both In_ and Out_ may be specified for the same argument.


Out
***

This boolean annotation is used to specify that the corresponding argument
(which should be a pointer type) is used by the function to return a value as
an element of a tuple.

For pointers to wrapped C structures or C++ class instances, ``char *`` and
``unsigned char *`` then this annotation must be explicitly specified if
required.

For pointers to other types then this annotation is assumed unless the In_
annotation is specified.

Both In_ and Out_ may be specified for the same argument.


Transfer
********

This boolean annotation is used to specify that ownership of the corresponding
argument (which should be a wrapped C structure or C++ class instance) is
transferred from Python to C++.  In addition, if the argument is of a class
method, then it is associated with the class instance with regard to the
cyclic garbage collector.

See `Ownership of Objects`_ for more detail.


TransferBack
************

This boolean annotation is used to specify that ownership of the corresponding
argument (which should be a wrapped C structure or C++ class instance) is
transferred back to Python from C++.  In addition, any association of the
argument with regard to the cyclic garbage collector with another instance is
removed.

Note that this can also be used as a function annotation.

See `Ownership of Objects`_ for more detail.


TransferThis
************

This boolean annotation is only used in C++ constructors or methods.  In the
context of a constructor or factory method it specifies that ownership of the
instance being created is transferred from Python to C++ if the corresponding
argument (which should be a wrapped C structure or C++ class instance) is not
``None``.  In addition, the newly created instance is associated with the
argument with regard to the cyclic garbage collector.

In the context of a non-factory method it specifies that ownership of ``this``
is transferred from Python to C++ if the corresponding argument is not
``None``.  If it is ``None`` then ownership is transferred to Python.

The annotation may be used more that once, in which case ownership is
transferred to last instance that is not ``None``.

See `Ownership of Objects`_ for more detail.


Class Annotations
-----------------

Abstract
********

This boolean annotation is used to specify that the class has additional pure
virtual methods that have not been specified and so it cannot be instantiated
or sub-classed from Python.


DelayDtor
*********

This boolean annotation is used to specify that the class's destructor should
not be called until the Python interpreter exits.  It would normally only be
applied to singleton classes.

When the Python interpreter exits the order in which any wrapped instances are
garbage collected is unpredictable.  However, the underlying C or C++ instances
may need to be destroyed in a certain order.  If this annotation is specified
then when the wrapped instance is garbage collected the C or C++ instance is
not destroyed but instead added to a list of delayed instances.  When the
interpreter exits then the function ``sipDelayedDtors`` is called with the
list of delayed instances.  ``sipDelayedDtors`` can then choose to call (or
ignore) the destructors in any desired order.

The ``sipDelayedDtors`` function must be specified using the `%ModuleCode`_
directive.  It's signature is as follows::

    static void sipDelayedDtors(const sipDelayedDtor *dd_list);

``dd_list`` is the linked list of delayed instances.  The following fields are
defined.

const char \*dd_name
    This is the name of the class excluding any package or module name.

void \*dd_ptr
    This is the address of the C or C++ instance to be destroyed.  It's exact
    type depends on the value of ``dd_isderived``.

int dd_isderived
    This is non-zero if the type of ``dd_ptr`` is actually the generated
    derived class.  This allows the correct destructor to be called.  See
    `Generated Derived Classes`_.

sipDelayedDtor \*dd_next
    This is the address of the next entry in the list or zero if this is the
    last one.

Note that the above applies only to C and C++ instances that are owned by
Python.


External
********

This boolean annotation is used to specify that the class is defined in another
module.  Declarations of external classes are private to the module in which
they appear.


NoDefaultCtors
**************

This boolean annotation is used to suppress the automatic generation of default
constructors for the class.


PyName
******

This name annotation specifies an alternative name for the class being wrapped
which is used when it is referred to from Python.  It is required when a class
name is the same as a Python keyword.  It may also be used to avoid name
clashes with other objects (e.g. enums, exceptions, functions) that have the
same name in the same C++ scope.


Enum Annotations
----------------

PyName
******

This name annotation specifies an alternative name for the enum or enum member
being wrapped which is used when it is referred to from Python.  It is required
when an enum or enum member name is the same as a Python keyword.  It may also
be used to avoid name clashes with other objects (e.g. classes, exceptions,
functions) that have the same name in the same C++ scope.


Exception Annotations
---------------------

PyName
******

This name annotation specifies an alternative name for the exception being
defined which is used when it is referred to from Python.  It is required when
an exception name is the same as a Python keyword.  It may also be used to
avoid name clashes with other objects (e.g. classes, enums, functions) that
have the same name.


Function Annotations
--------------------

AutoGen
*******

This optional name annotation is used with class methods to specify that the
method be automatically included in all sub-classes.  The value is the name of
a feature (specified using the `%Feature`_ directive) which must be enabled
for the method to be generated.


Default
*******

This boolean annotation is only used with C++ constructors.  Sometimes SIP
needs to create a class instance.  By default it uses a constructor with no
compulsory arguments if one is specified.  (SIP will automatically generate a
constructor with no arguments if no constructors are specified.)  This
annotation is used to explicitly specify which constructor to use.  Zero is
passed as the value of any arguments to the constructor.


Factory
*******

This boolean annotation specifies that the value returned by the function
(which should be a wrapped C structure or C++ class instance) is a newly
created instance and is owned by Python.

See `Ownership of Objects`_ for more detail.


HoldGIL
*******

This boolean annotation specifies that the Python Global Interpreter Lock (GIL)
is not released before the call to the underlying C or C++ function.  See
`The Python Global Interpreter Lock`_ and the ReleaseGIL_ annotation.


NewThread
*********

This boolean annotation specifies that the function will create a new thread.


NoDerived
*********

This boolean annotation is only used with C++ constructors.  In many cases SIP
generates a derived class for each class being wrapped (see `Generated Derived
Classes`_).  This derived class contains constructors with the same C++
signatures as the class being wrapped.  Sometimes you may want to define a
Python constructor that has no corresponding C++ constructor.  This annotation
is used to suppress the generation of the constructor in the derived class.


Numeric
*******

This boolean annotation specifies that the operator should be interpreted as a
numeric operator rather than a sequence operator.  Python uses the ``+``
operator for adding numbers and concatanating sequences, and the ``*`` operator
for multiplying numbers and repeating sequences.  SIP tries to work out which
is meant by looking at other operators that have been defined for the type.
If it finds either ``-``, ``-=``, ``/``, ``/=``, ``%`` or ``%=`` defined then
it assumes that ``+``, ``+=``, ``*`` and ``*=`` should be numeric operators.
Otherwise, if it finds either ``[]``, ``__getitem__()``, ``__setitem__()`` or
``__delitem__()`` defined then it assumes that they should be sequence
operators.  This annotation is used to force SIP to treat the operator as
numeric.


PostHook
********

This name annotation is used to specify the name of a Python builtin that is
called immediately after the call to the underlying C or C++ function or any
handwritten code.  The builtin is not called if an error occurred.  It is
primarily used to integrate with debuggers.


PreHook
*******

This name annotation is used to specify the name of a Python builtin that is
called immediately after the function's arguments have been successfully
parsed and before the call to the underlying C or C++ function or any
handwritten code.  It is primarily used to integrate with debuggers.


PyName
******

This name annotation specifies an alternative name for the function being
wrapped which is used when it is referred to from Python.  It is required when
a function or method name is the same as a Python keyword.  It may also be used
to avoid name clashes with other objects (e.g. classes, enums, exceptions) that
have the same name in the same C++ scope.


ReleaseGIL
**********

This boolean annotation specifies that the Python Global Interpreter Lock (GIL)
is released before the call to the underlying C or C++ function and reacquired
afterwards.  It should be used for functions that might block or take a
significant amount of time to execute.  See `The Python Global Interpreter
Lock`_ and the HoldGIL_ annotation.


TransferBack
************

This boolean annotation specifies that ownership of the value returned by the
function (which should be a wrapped C structure or C++ class instance) is
transferred back to Python from C++.  Normally returned values (unless they are
new references to already wrapped values) are owned by C++.  In addition, any
association of the returned value with regard to the cyclic garbage collector
with another instance is removed.

Note that this can also be used as an argument annotation.

See `Ownership of Objects`_ for more detail.


License Annotations
-------------------

Licensee
********

This optional string annotation specifies the license's licensee.  No
restrictions are placed on the contents of the string.

See the `%License`_ directive.


Signature
*********

This optional string annotation specifies the license's signature.  No
restrictions are placed on the contents of the string.

See the `%License`_ directive.


Timestamp
*********

This optional string annotation specifies the license's timestamp.  No
restrictions are placed on the contents of the string.

See the `%License`_ directive.


Type
****

This string annotation specifies the license's type.  No restrictions are
placed on the contents of the string.

See the `%License`_ directive.


Variable Annotations
--------------------

PyName
******

This name annotation specifies an alternative name for the variable being
wrapped which is used when it is referred to from Python.  It is required when
a variable name is the same as a Python keyword.  It may also be used to avoid
name clashes with other objects (e.g. classes, functions) that have the same
name in the same C++ scope.


SIP API for Handwritten Code
============================

In this section we describe the API that can be used by handwritten code in
specification files.


SIP_API_MAJOR_NR
----------------

This is a C preprocessor symbol that defines the major number of the SIP API.
Its value is a number.  There is no direct relationship between this and the
SIP version number.


SIP_API_MINOR_NR
----------------

This is a C preprocessor symbol that defines the minor number of the SIP API.
Its value is a number.  There is no direct relationship between this and the
SIP version number.


SIP_BLOCK_THREADS
-----------------

This is a C preprocessor macro that will make sure the Python Global
Interpreter Lock (GIL) is acquired.  Python API calls must only be made when
the GIL has been acquired.  There must be a corresponding
`SIP_UNBLOCK_THREADS`_ at the same lexical scope.


SIP_SSIZE_T
-----------

This is a C preprocessor macro that is defined as ``Py_ssize_t`` for Python
v2.5 and later, and as ``int`` for earlier versions of Python.  It makes it
easier to write PEP 353 compliant handwritten code.


SIP_UNBLOCK_THREADS
-------------------

This is a C preprocessor macro that will restore the Python Global Interpreter
Lock (GIL) to the state it was prior to the corresponding `SIP_BLOCK_THREADS`_.


SIP_VERSION
-----------

This is a C preprocessor symbol that defines the SIP version number
represented as a 3 part hexadecimal number (e.g. v4.0.0 is represented as
``0x040000``).


SIP_VERSION_STR
---------------

This is a C preprocessor symbol that defines the SIP version number
represented as a string.  For development snapshots it will start with
``snapshot-``.


sipBadCatcherResult()
---------------------

void sipBadCatcherResult(PyObject \*method)
    This raises a Python exception when the result of a Python reimplementation
    of a C++ method doesn't have the expected type.  It is normally called by
    handwritten code specified with the `%VirtualCatcherCode`_ directive.
    *method* is the Python method and would normally be the supplied
    ``sipMethod``.


sipBadLengthForSlice()
----------------------

void sipBadLengthForSlice(SIP_SSIZE_T seqlen, SIP_SSIZE_T slicelen)
    This raises a Python exception when the length of a slice object is
    inappropriate for a sequence-like object.  It is normally called by
    handwritten code specified for ``__setitem__()`` methods.  *seqlen* is the
    length of the sequence.  *slicelen* is the length of the slice.  With
    versions of Python prior to v2.5 the arguments have type ``int``.


sipBuildResult()
----------------

PyObject \*sipBuildResult(int \*iserr, const char \*format, ...)
    This creates a Python object based on a format string and associated
    values in a similar way to the Python ``Py_BuildValue()`` function.  If
    there was an error then ``NULL`` is returned and a Python exception is
    raised.  If *iserr* is not ``NULL`` then the location it points to is set
    to a non-zero value.  *format* is the string of format characters.

    If *format* begins and ends with parentheses then a tuple of objects is
    created.  If *format* contains more than one format character then
    parentheses must be specified.

    In the following description the first letter is the format character, the
    entry in parentheses is the Python object type that the format character
    will create, and the entry in brackets are the types of the C/C++ values
    to be passed. 

    ``a`` (string) [char \*, int]
        Convert a C/C++ character array and its length to a Python string.  If
        the array is ``NULL`` then the length is ignored and the result is
        ``Py_None``.

    ``b`` (boolean) [int]
        Convert a C/C++ ``int`` to a Python boolean.

    ``c`` (string) [char]
        Convert a C/C++ ``char`` to a Python string.

    ``d`` (float) [double]
        Convert a C/C++ ``double`` to a Python floating point number.

    ``e`` (integer) [enum]
        Convert an anonymous C/C++ ``enum`` to a Python integer.

    ``f`` (float) [float]
        Convert a C/C++ ``float`` to a Python floating point number.

    ``h`` (integer) [short]
        Convert a C/C++ ``short`` to a Python integer.

    ``i`` (integer) [int]
        Convert a C/C++ ``int`` to a Python integer.

    ``l`` (long) [long]
        Convert a C/C++ ``long`` to a Python integer.

    ``m`` (long) [unsigned long]
        Convert a C/C++ ``unsigned long`` to a Python long.

    ``n`` (long) [long long]
        Convert a C/C++ ``long long`` to a Python long.

    ``o`` (long) [unsigned long long]
        Convert a C/C++ ``unsigned long long`` to a Python long.

    ``s`` (string) [char \*]
        Convert a C/C++ ``'\0'`` terminated string to a Python string.  If the
        string pointer is ``NULL`` then the result is ``Py_None``.

    ``t`` (long) [unsigned short]
        Convert a C/C++ ``unsigned short`` to a Python long.

    ``u`` (long) [unsigned int]
        Convert a C/C++ ``unsigned int`` to a Python long.

    ``w`` (unicode) [wchar_t]
        Convert a C/C++ wide character to a Python unicode object.

    ``x`` (unicode) [wchar_t \*]
        Convert a C/C++ ``L'\0'`` terminated wide character string to a Python
        unicode object.  If the string pointer is ``NULL`` then the result is
        ``Py_None``.

    ``A`` (unicode) [wchar_t \*, int]
        Convert a C/C++ wide character array and its length to a Python unicode
        object.  If the array is ``NULL`` then the length is ignored and the
        result is ``Py_None``.

    ``B`` (wrapped instance) [*type* \*, sipWrapperType \*, PyObject \*]
        Convert a new C structure or a new C++ class instance to a Python class
        instance object.  Ownership of the structure or instance is determined
        by the ``PyObject *`` argument.  If it is ``NULL`` and the instance has
        already been wrapped then the ownership is unchanged.  If it is
        ``NULL`` or ``Py_None`` then ownership will be with Python.  Otherwise
        ownership will be with C/C++ and the instance associated with the
        ``PyObject *`` argument.  The Python class is influenced by any
        applicable `%ConvertToSubClassCode`_ code.

    ``C`` (wrapped instance) [*type* \*, sipWrapperType \*, PyObject \*]
        Convert a C structure or a C++ class instance to a Python class
        instance object.  If the structure or class instance has already been
        wrapped then the result is a new reference to the existing class
        instance object.  Ownership of the structure or instance is determined
        by the ``PyObject *`` argument.  If it is ``NULL`` and the instance has
        already been wrapped then the ownership is unchanged.  If it is
        ``NULL`` and the instance is newly wrapped then ownership will be with
        C/C++.  If it is ``Py_None`` then ownership is transferred to Python
        via a call to `sipTransferBack()`_.  Otherwise ownership is transferred
        to C/C++ and the instance associated with the ``PyObject *`` argument
        via a call to `sipTransferTo()`_.  The Python class is influenced by
        any applicable `%ConvertToSubClassCode`_ code.

    ``D`` (object) [*type* \*, const sipMappedType \*, PyObject \*]
        Convert a C structure or a C++ class instance wrapped as a mapped type
        to a Python object.  Ownership of the structure or instance is
        determined by the ``PyObject *`` argument.  If it is ``NULL`` then the
        ownership is unchanged.  If it is ``Py_None`` then ownership is
        transferred to Python via a call to `sipTransferBack()`_.  Otherwise
        ownership is transferred to C/C++ and the instance associated with the
        ``PyObject *`` argument via a call to `sipTransferTo()`_.

    ``E`` (wrapped enum) [enum, PyTypeObject \*]
        Convert a named C/C++ ``enum`` to an instance of the corresponding
        Python named enum type.

    ``M`` (wrapped instance) [*type* \*, sipWrapperType \*]
        Convert a C structure or a C++ class instance to a Python class
        instance object.  If the structure or class instance has already been
        wrapped then the result is a new reference to the existing class
        instance object.  If the instance has already been wrapped then the
        ownership is unchanged.  If the instance is newly wrapped then
        ownership will be with C/C++.  The Python class is influenced by any
        applicable `%ConvertToSubClassCode`_ code.  This is deprecated from
        SIP v4.4.

    ``N`` (wrapped instance) [*type* \*, sipWrapperType \*]
        Convert a C structure or a C++ class instance to a Python class
        instance object.  This should not be used if the structure or class
        instance might already have been wrapped.  Ownership of the structure
        or instance will be with Python.  The Python class is influenced by
        any applicable `%ConvertToSubClassCode`_ code.  This is deprecated
        from SIP v4.4.

    ``O`` (wrapped instance) [*type* \*, sipWrapperType \*]
        Convert a C structure or a C++ class instance to a Python class
        instance object.  If the structure or class instance has already been
        wrapped then the result is a new reference to the existing class
        instance object.  Ownership of the structure or instance will be with
        C/C++.  This is deprecated from SIP v4.4.

    ``P`` (wrapped instance) [*type* \*, sipWrapperType \*]
        Convert a C structure or a C++ class instance to a Python class
        instance object.  This should not be used if the structure or class
        instance might already have been wrapped.  Ownership of the structure
        or instance will be with Python.  This is deprecated from SIP v4.4.

    ``R`` (object) [PyObject \*]
        The result is value passed without any conversions.  The reference
        count is unaffected, i.e. a reference is taken.

    ``S`` (object) [PyObject \*]
        The result is value passed without any conversions.  The reference
        count is incremented.

    ``T`` (object) [void \*, PyObject \*(\*)(void \*cppptr)]
        Convert a C structure or a C++ class instance to a Python object using
        a convertor function.  See `Generated Type Convertors`_.  This is
        deprecated from SIP v4.4.

    ``V`` (sip.voidptr) [void \*]
        Convert a C/C++ ``void *`` Python ``sip.voidptr`` object.


sipCallMethod()
---------------

PyObject \*sipCallMethod(int \*iserr, PyObject \*method, const char \*format, ...)
    This calls a Python method passing a tuple of arguments based on a format
    string and associated values in a similar way to the Python
    ``PyObject_CallObject()`` function.  If there was an error then ``NULL`` is
    returned and a Python exception is raised.  If *iserr* is not ``NULL``
    then the location it points to is set to a non-zero value.  *method* is the
    Python bound method to call.  *format* is the string of format characters
    (see `sipBuildResult()`_).

    This is normally called by handwritten code specified with the
    `%VirtualCatcherCode`_ directive with *method* being the supplied
    ``sipMethod``.


sipCanConvertToInstance()
-------------------------

int sipCanConvertToInstance(PyObject \*obj, sipWrapperType \*type, int flags)
    This returns a non-zero value if a Python object can be converted to an
    instance of a C structure or C++ class.  *obj* is the Python object.
    *type* is the generated type corresponding to the C/C++ type being checked.
    *flags* is any combination of the following values used to fine tune the
    check.

        - ``SIP_NOT_NONE`` causes the check to fail if *obj* is ``None``.

        - ``SIP_NO_CONVERTORS`` suppresses the use of of any
          `%ConvertToTypeCode`_ for *type*.


sipCanConvertToMappedType()
---------------------------

int sipCanConvertToMappedType(PyObject \*obj, const sipMappedType \*mt, int flags)
    This returns a non-zero value if a Python object can be converted to an
    instance of a C structure or C++ class which has been implemented as a
    mapped type.  *obj* is the Python object.  *mt* is an opaque structure
    returned by `sipFindMappedType()`_.  *flags* is any combination of the
    following values used to fine tune the check.

        - ``SIP_NOT_NONE`` causes the check to fail if *obj* is ``None``.


sipClassName()
--------------

PyObject \*sipClassName(PyObject \*obj)
    This returns the class name of a wrapped instance as a Python string.  It
    comes with a reference.


sipConnectRx()
--------------

PyObject \*sipConnectRx(PyObject \*sender, const char \*signal, PyObject \*receiver, const char \*slot, int type)
    This connects a signal to a signal or slot and returns ``Py_True`` if the
    signal was connected or ``Py_False`` if not.  If there was some other
    error then a Python exception is raised and ``NULL`` is returned.  *sender*
    is the wrapped ``QObject`` derived instance that emits the signal.
    *signal* is the typed name of the signal.  *receiver* is the wrapped
    ``QObject`` derived instance or Python callable that the signal is
    connected to.  *slot* is the typed name of the slot, or ``NULL`` if
    *receiver* is a Python callable.  *type* is the type of connection and is
    cast from Qt::ConnectionType.  It is normally only used by PyQt to
    implement ``QObject.connect()``.


sipConvertFromInstance()
------------------------

PyObject \*sipConvertFromInstance(void \*cpp, sipWrapperType \*type, PyObject \*transferObj)
    Convert a C structure or a C++ class instance to a Python class instance
    object.  *cpp* is the C/C++ instance.  If the instance has already been
    wrapped then the result is a new reference to the existing instance object.
    *type* is the generated type corresponding to the C/C++ type.
    *transferObj* controls the ownership of the returned value.  If the
    structure or class instance has already been wrapped then the result is a
    new reference to the existing class instance object.  If it is ``NULL`` and
    the instance has already been wrapped then the ownership is unchanged.  If
    it is ``NULL`` and the instance is newly wrapped then ownership will be
    with C/C++.  If it is ``Py_None`` then ownership is transferred to Python
    via a call to `sipTransferBack()`_.  Otherwise ownership is transferred to
    C/C++ and the instance associated with *transferObj* via a call to
    `sipTransferTo()`_.  The Python class is influenced by any applicable
    `%ConvertToSubClassCode`_ code.


sipConvertFromMappedType()
--------------------------

PyObject \*sipConvertFromMappedType(void \*cpp, const sipMappedType \*mt, PyObject \*transferObj)
    Convert a C structure or a C++ class instance wrapped as a mapped type to a
    Python object.  *cpp* is the C/C++ instance.  *mt* is the opaque structure
    returned by `sipFindMappedType()`_.  *transferObj* controls any ownership
    changes to *obj*.  If it is ``NULL`` then the ownership is unchanged.  If
    it is ``Py_None`` then ownership is transferred to Python via a call to
    `sipTransferBack()`_.  Otherwise ownership is transferred to C/C++ and the
    instance associated with the ``PyObject *`` argument via a call to
    `sipTransferTo()`_.


sipConvertFromNamedEnum()
-------------------------

PyObject \*sipConvertFromNamedEnum(int eval, PyTypeObject \*type)
    Convert a named C/C++ ``enum`` to an instance of the corresponding Python
    named enum type.  *eval* is the enumerated value to convert.  *type* is the
    generated Python type object (see `Generated Named Enum Type Objects`_).


sipConvertFromNewInstance()
---------------------------

PyObject \*sipConvertFromNewInstance(void \*cpp, sipWrapperType \*type, PyObject \*transferObj)
    Convert a new C structure or a new C++ class instance to a Python class
    instance object.  *cpp* is the C/C++ instance.  *type* is the generated
    type corresponding to the C/C++ type.  *transferObj* controls the ownership
    of the returned value.  If it is ``NULL`` or ``Py_None`` then ownership
    will be with Python.  Otherwise ownership will be with C/C++ and the
    instance associated with *transferObj*.  The Python class is influenced by
    any applicable `%ConvertToSubClassCode`_ code.


sipConvertFromSequenceIndex()
-----------------------------

SIP_SSIZE_T sipConvertFromSequenceIndex(SIP_SSIZE_T idx, SIP_SSIZE_T len)
    This converts a Python sequence index (i.e. where a negative value refers
    to the offset from the end of the sequence) to a C/C++ array index.  If the
    index was out of range then a negative value is returned and a Python
    exception raised.  With versions of Python prior to v2.5 the result and the
    arguments have type ``int``.


sipConvertFromSliceObject()
---------------------------

int sipConvertFromSliceObject(PyObject \*slice, SIP_SSIZE_T length, SIP_SSIZE_T \*start, SIP_SSIZE_T \*stop, SIP_SSIZE_T \*step, SIP_SSIZE_T \*slicelength)
    This is a thin wrapper around the Python ``PySlice_GetIndicesEx()``
    function provided to make it easier to write handwritten code that is
    compatible with SIP v3.x and versions of Python earlier that v2.3.


sipConvertToCpp()
-----------------

void \*sipConvertToCpp(PyObject \*obj, sipWrapperType \*type, int \*iserr)
    This function is deprecated from SIP v4.4.  It is equivalent to::

        sipConvertToInstance(obj, type, NULL, SIP_NO_CONVERTORS, NULL, iserr);


sipConvertToInstance()
----------------------

void \*sipConvertToInstance(PyObject \*obj, sipWrapperType \*type, PyObject \*transferObj, int flags, int \*state, int \*iserr)
    This converts a Python object to an instance of a C structure or C++ class
    assuming that a previous call to `sipCanConvertToInstance()`_ has been
    successful.  *obj* is the Python object.  *type* is the generated type
    corresponding to the C/C++ type returned.  It may be any class in the
    object's class hierarchy.  *transferObj* controls any ownership changes to
    *obj*.  If it is ``NULL`` then the ownership is unchanged.  If it is
    ``Py_None`` then ownership is transferred to Python via a call to
    `sipTransferBack()`_.  Otherwise ownership is transferred to C/C++ and
    *obj* associated with *transferObj* via a call to `sipTransferTo()`_.
    *flags* is any combination of the following values used to fine tune the
    check.

        - ``SIP_NOT_NONE`` causes the check to fail if *obj* is ``None``.

        - ``SIP_NO_CONVERTORS`` suppresses the use of of any
          `%ConvertToTypeCode`_ for *type*.

    If *state* is not ``NULL`` then the location it points to is set to
    describe the state of the returned C/C++ instance and is the value returned
    by any `%ConvertToTypeCode`_.  The calling code must then release the value
    at some point to prevent a memory leak by calling `sipReleaseInstance()`_.
    If there is an error then the location *iserr* points to is set to a
    non-zero value.  If it was initially a non-zero value then the conversion
    isn't attempted in the first place.  (This allows several calls to be made
    that share the same error flag so that it only needs to be tested once
    rather than after each call.)


sipConvertToMappedType()
------------------------

void \*sipConvertToMappedType(PyObject \*obj, const sipMappedType \*mt, PyObject \*transferObj, int flags, int \*state, int \*iserr)
    This converts a Python object to an instance of a C structure or C++
    class that is implemented as a mapped type assuming that a previous call to
    `sipCanConvertToMappedType()`_ has been successful.  *obj* is the Python
    object.  *mt* is the opaque structure returned by `sipFindMappedType()`_.
    *transferObj* controls any ownership changes to *obj*.  If it is ``NULL``
    then the ownership is unchanged.  If it is ``Py_None`` then ownership is
    transferred to Python via a call to `sipTransferBack()`_.  Otherwise
    ownership is transferred to C/C++ and *obj* associated with *transferObj*
    via a call to `sipTransferTo()`_.  *flags* is any combination of the
    following values used to fine tune the check.

        - ``SIP_NOT_NONE`` causes the check to fail if *obj* is ``None``.

    If *state* is not ``NULL`` then the location it points to is set to
    describe the state of the returned C/C++ instance and is the value returned
    by any `%ConvertToTypeCode`_.  The calling code must then release the value
    at some point to prevent a memory leak by calling
    `sipReleaseMappedType()`_.  If there is an error then the location *iserr*
    points to is set to a non-zero value.  If it was initially a non-zero value
    then the conversion isn't attempted in the first place.  (This allows
    several calls to be made that share the same error flag so that it only
    needs to be tested once rather than after each call.)


sipDisconnectRx()
-----------------

PyObject \*sipDisconnectRx(PyObject \*sender, const char \*signal, PyObject \*receiver, const char \*slot)
    This disconnects a signal from a signal or slot and returns ``Py_True`` if
    the signal was disconnected or ``Py_False`` if not.  If there was some
    other error then a Python exception is raised and ``NULL`` is returned.
    *sender* is the wrapped ``QObject`` derived instance that emits the signal.
    *signal* is the typed name of the signal.  *receiver* is the wrapped
    ``QObject`` derived instance or Python callable that the signal is
    connected to.  *slot* is the typed name of the slot, or ``NULL`` if
    *receiver* is a Python callable.  It is normally only used by PyQt to
    implement ``QObject.disconnect()``.


sipEmitSignal()
---------------

int sipEmitSignal(PyObject \*txobj, const char \*signal, PyObject \*args)
    This emits a signal and returns zero if there was no error.  If there was
    an error then a Python exception is raised and a negative value is
    returned.  *txobj* is the wrapped ``QObject`` derived instance that emits
    the signal.  *signal* is the typed name of the signal.  *args* is a Python
    tuple of the signal arguments.  It is normally only used by PyQt to
    implement ``QObject.emit()``.


sipExportSymbol()
-----------------

int sipExportSymbol(const char \*name, void \*sym)
    Python does not allow extension modules to directly access symbols in
    another extension module.  This exports a symbol, referenced by a name,
    that can subsequently be imported, using `sipImportSymbol()`_, by another
    module.  *name* is the name of the symbol and *sym* is its value.  Zero is
    returned if there was no error.  A negative value is returned if *name* is
    already associated with a symbol or there was some other error.


sipFindClass()
--------------

sipWrapperType \*sipFindClass(const char \*type)
    This returns a pointer to the generated type corresponding to a C/C++ type.
    *type* is the C/C++ declaration of the type.  ``NULL`` is returned if the
    C/C++ type doesn't exist.  The value of the pointer will not change and
    may be saved in a static cache.


sipFindMappedType()
-------------------

const sipMappedType \*sipFindMappedType(const char \*type)
    This returns a pointer to an opaque structure describing a mapped type.
    *type* is the C/C++ declaration of the type.  ``NULL`` is returned if the
    mapped type doesn't exist.  The value of the pointer will not change and
    may be saved in a static cache.


sipFindNamedEnum()
------------------

PyTypeObject \*sipFindNamedEnum(const char \*type)
    This returns a pointer to the generated type corresponding to a named C/C++
    enum.  *type* is the C/C++ declaration of the enum.  ``NULL`` is returned
    if the named C/C++ enum doesn't exist.  The value of the pointer will not
    change and may be saved in a static cache.


sipForceConvertToInstance()
---------------------------

void \*sipForceConvertToInstance(PyObject \*obj, sipWrapperType \*type, PyObject \*transferObj, int flags, int \*state, int \*iserr)
    This converts a Python object to an instance of a C structure or C++ class
    by calling `sipCanConvertToInstance()`_ and, if it is successfull, calling
    `sipConvertToInstance()`_.  See `sipConvertToInstance()`_ for a full
    description of the arguments.


sipForceConvertToMappedType()
-----------------------------

void \*sipForceConvertToMappedType(PyObject \*obj, const sipMappedType \*mt, PyObject \*transferObj, int flags, int \*state, int \*iserr)
    This converts a Python object to an instance of a C structure or C++ class
    which has been implemented as a mapped type by calling
    `sipCanConvertToMappedType()`_ and, if it is successfull, calling
    `sipConvertToMappedType()`_.  See `sipConvertToMappedType()`_ for a full
    description of the arguments.


sipFree()
---------

void sipFree(void \*mem)
    This returns an area of memory allocated by `sipMalloc()`_ to the heap.
    *mem* is a pointer to the area of memory.


sipGetSender()
--------------

const void \*sipGetSender()
    This returns a pointer to the last ``QObject`` instance that emitted a Qt
    signal.  It is normally only used by PyQt to implement
    ``QObject.sender()``.


sipGetWrapper()
---------------

PyObject \*sipGetWrapper(void \*cppptr, sipWrapperType \*type)
    This returns a borrowed reference to the wrapped instance object for a C
    structure or C++ class instance.  If the structure or class instance
    hasn't been wrapped then ``NULL`` is returned (and no Python exception is
    raised).  *cppptr* is the pointer to the structure or class instance.
    *type* is the generated type corresponding to the C/C++ type.


sipImportSymbol()
-----------------

void \*sipImportSymbol(const char \*name)
    Python does not allow extension modules to directly access symbols in
    another extension module.  This imports a symbol, referenced by a name,
    that has previously been exported, using `sipExportSymbol()`_, by another
    module.  *name* is the name of the symbol.  The value of the symbol is
    returned if there was no error.  ``NULL`` is returned if there is no such
    symbol.


sipIntTypeClassMap
------------------

This C structure is used with `sipMapIntToClass()`_ to define a mapping
between integer based RTTI and `generated type objects`_.  The structure
elements are as follows.

int typeInt
    The integer RTTI.

sipWrapperType \*\*pyType.
    A pointer to the corresponding Python type object.


sipIsSubClassInstance()
-----------------------

int sipIsSubClassInstance(PyObject \*obj, sipWrapperType \*type)
    This function is deprecated from SIP v4.4.  It is equivalent to::

        sipCanConvertToInstance(obj, type, SIP_NOT_NONE | SIP_NO_CONVERTORS);


sipLong_AsUnsignedLong()
------------------------

unsigned long sipLong_AsUnsignedLong(PyObject \*obj)
    This function is a thin wrapper around PyLong_AsUnsignedLong() that works
    around a bug in Python v2.3.x and earlier when converting integer objects.


sipMalloc()
-----------

void \*sipMalloc(size_t nbytes)
    This allocates an area of memory of size *nytes* on the heap using the
    Python ``PyMem_Malloc()`` function.  If there was an error then ``NULL`` is
    returned and a Python exception raised.  See `sipFree()`_.


sipMapIntToClass()
------------------

sipWrapperType \*sipMapIntToClass(int type, const sipIntTypeClassMap \*map, int maplen)
    This is used in `%ConvertToSubClassCode`_ code as a convenient way of
    converting integer based RTTI to the corresponding Python type object.
    *type* is the RTTI.  *map* is the table of known RTTI and the corresponding
    type objects (see sipIntTypeClassMap_).  The entries in the table must be
    sorted in ascending order of RTTI.  *maplen* is the number of entries in
    the table.  The corresponding Python type object is returned, or ``NULL``
    if *type* wasn't in *map*.


sipMapStringToClass()
---------------------

sipWrapperType \*sipMapStringToClass(char \*type, const sipStringTypeClassMap \*map, int maplen)
    This is used in `%ConvertToSubClassCode`_ code as a convenient way of
    converting ``'\0'`` terminated string based RTTI to the corresponding
    Python type object.  *type* is the RTTI.  *map* is the table of known RTTI
    and the corresponding type objects (see sipStringTypeClassMap_).  The
    entries in the table must be sorted in ascending order of RTTI.  *maplen*
    is the number of entries in the table.  The corresponding Python type
    object is returned, or ``NULL`` if *type* wasn't in *map*.


sipParseResult()
----------------

int sipParseResult(int \*iserr, PyObject \*method, PyObject \*result, const char \*format, ...)
    This converts a Python object (usually returned by a method) to C/C++ based
    on a format string and associated values in a similar way to the Python
    ``PyArg_ParseTuple()`` function.  If there was an error then a negative
    value is returned and a Python exception is raised.  If *iserr* is not
    ``NULL`` then the location it points to is set to a non-zero value.
    *method* is the Python bound method that returned the *result* object.
    *format* is the string of format characters.

    This is normally called by handwritten code specified with the
    `%VirtualCatcherCode`_ directive with *method* being the supplied
    ``sipMethod`` and ``result`` being the value returned by
    `sipCallMethod()`_.

    If *format* begins and ends with parentheses then *result* must be a Python
    tuple and the rest of *format* is applied to the tuple contents.

    In the following description the first letter is the format character, the
    entry in parentheses is the Python object type that the format character
    will convert, and the entry in brackets are the types of the C/C++ values
    to be passed. 

    ``a`` (string) [char \*\*, int \*]
        Convert a Python string to a C/C++ character array and its length.  If
        the Python object is ``Py_None`` then the array and length are ``NULL``
        and zero respectively.

    ``b`` (integer) [bool \*]
        Convert a Python integer to a C/C++ ``bool``.

    ``c`` (string) [char \*]
        Convert a Python string of length 1 to a C/C++ ``char``.

    ``d`` (float) [double \*]
        Convert a Python floating point number to a C/C++ ``double``.

    ``e`` (integer) [enum \*]
        Convert a Python integer to an anonymous C/C++ ``enum``.

    ``f`` (float) [float \*]
        Convert a Python floating point number to a C/C++ ``float``.

    ``h`` (integer) [short \*]
        Convert a Python integer to a C/C++ ``short``.

    ``i`` (integer) [int \*]
        Convert a Python integer to a C/C++ ``int``.

    ``l`` (long) [long \*]
        Convert a Python long to a C/C++ ``long``.

    ``m`` (long) [unsigned long \*]
        Convert a Python long to a C/C++ ``unsigned long``.

    ``n`` (long) [long long \*]
        Convert a Python long to a C/C++ ``long long``.

    ``o`` (long) [unsigned long long \*]
        Convert a Python long to a C/C++ ``unsigned long long``.

    ``s`` (string) [char \*\*]
        Convert a Python string to a C/C++ ``'\0'`` terminated string.  If the
        Python object is ``Py_None`` then the string is ``NULL``.

    ``t`` (long) [unsigned short \*]
        Convert a Python long to a C/C++ ``unsigned short``.

    ``u`` (long) [unsigned int \*]
        Convert a Python long to a C/C++ ``unsigned int``.

    ``w`` (unicode) [wchar_t \*]
        Convert a Python unicode object of length 1 to a C/C++ wide character.

    ``x`` (unicode) [wchar_t \*\*]
        Convert a Python unicode object to a C/C++ ``L'\0'`` terminated wide
        character string.  If the Python object is ``Py_None`` then the string
        is ``NULL``.

    ``A`` (unicode) [wchar_t \*\*, int \*]
        Convert a Python unicode object to a C/C++ wide character array and its
        length.  If the Python object is ``Py_None`` then the array and length
        are ``NULL`` and zero respectively.

    ``Cf`` (wrapped class) [sipWrapperType \*, int \*, void \*\*]
        Convert a Python object to a C structure or a C++ class instance and
        return its state as described in `sipConvertToInstance()`_.  ``f`` is a
        combination of the following flags encoded as an ASCII character by
        adding ``0`` to the combined value:

            0x01 disallows the conversion of ``Py_None`` to ``NULL``

            0x02 implements the `Factory`_ annotation

            0x04 suppresses the return of the state of the returned C/C++
                 instance.  Note that the ``int *`` used to return the state is
                 not passed if this flag is specified.

    ``Df`` (mapped type) [const sipMappedType \*, int \*, void \*\*]
        Convert a Python object to a C structure or a C++ class instance
        implemented as a mapped type and return its state as described in
        `sipConvertToMappedType()`_.  ``f`` is a combination of the following
        flags encoded as an ASCII character by adding ``0`` to the combined
        value:

            0x01 disallows the conversion of ``Py_None`` to ``NULL``

            0x02 implements the `Factory`_ annotation

            0x04 suppresses the return of the state of the returned C/C++
                 instance.  Note that the ``int *`` used to return the state is
                 not passed if this flag is specified.

    ``E`` (wrapped enum) [PyTypeObject \*, enum \*]
        Convert a Python named enum type to the corresponding C/C++ ``enum``.

    ``L`` (object) [*type* \*(\*)(PyObject \*obj, int \*iserr), void \*\*]
        Convert a Python object to a C structure or a C++ class instance using
        a convertor function.  See `Generated Type Convertors`_.  This is
        deprecated from SIP v4.4.

    ``M`` (object) [*type* \*(\*)(PyObject \*obj, int \*iserr), void \*\*]
        Convert a Python object to a C structure or a C++ class instance using
        a convertor function.  If the structure or class instance pointer is
        ``NULL`` then return an error.  See `Generated Type Convertors`_.  This
        is deprecated from SIP v4.4.

    ``N`` (object) [PyTypeObject \*, PyObject \*\*]
        A Python object is checked to see if it is a certain type and then
        returned without any conversions.  The reference count is incremented.
        The Python object may be ``Py_None``.

    ``O`` (object) [PyObject \*\*]
        A Python object is returned without any conversions.  The reference
        count is incremented.

    ``T`` (object) [PyTypeObject \*, PyObject \*\*]
        A Python object is checked to see if it is a certain type and then
        returned without any conversions.  The reference count is incremented.
        The Python object may not be ``Py_None``.

    ``V`` (sip.voidptr) [void \*]
        Convert a Python ``sip.voidptr`` object to a C/C++ ``void *``.

    ``Z`` (object) []
        Check that a Python object is ``Py_None``.  No value is returned.


sipReleaseInstance()
--------------------

void sipReleaseInstance(void \*cpp, sipWrapperType \*type, int state)
    This destroys a wrapped C/C++ instance if it was a temporary instance.  It
    is called after a call to either `sipConvertToInstance()`_ or
    `sipForceConvertToInstance()`_.  *cpp* is the wrapped C/C++ instance.
    *type* is the generated type corresponding to *cpp*.  *state* describes the
    state of the instance.


sipReleaseMappedType()
----------------------

void sipReleaseMappedType(void \*cpp, const sipMappedType \*mt, int state)
    This destroys a wrapped C/C++ mapped type if it was a temporary instance.
    It is called after a call to either `sipConvertToMappedType()`_ or
    `sipForceConvertToMappedType()`_.  *cpp* is the wrapped C/C++ instance.
    *mt* is the opaque structure returned by `sipFindMappedType()`_.  *state*
    describes the state of the instance.


sipStringTypeClassMap
---------------------

This C structure is used with `sipMapStringToClass()`_ to define a mapping
between ``'\0'`` terminated string based RTTI and `generated type objects`_.
The structure elements are as follows.

char \*typeString
    The ``'\0'`` terminated string RTTI.

sipWrapperType \*\*pyType.
    A pointer to the corresponding Python type object.


sipTransfer()
-------------

void sipTransfer(PyObject \*obj, int tocpp)
    This function is deprecated from SIP v4.3.  If *tocpp* is non-zero then the
    equivalent call is::

        sipTransferTo(obj, obj);

    If *tocpp* is zero then the equivalent call is::

        sipTransferBack(obj);


sipTransferBack()
-----------------

void sipTransferBack(PyObject \*obj)
    This transfers ownership of a Python wrapped instance to Python (see
    `Ownership of Objects`_).  *obj* is the wrapped instance.  In addition,
    any association of the instance with regard to the cyclic garbage
    collector with another instance is removed.


sipTransferTo()
---------------

void sipTransferTo(PyObject \*obj, PyObject \*owner)
    This transfers ownership of a Python wrapped instance to C++ (see
    `Ownership of Objects`_).  *obj* is the wrapped instance.  *owner* is an
    optional wrapped instance that *obj* becomes associated with with regard
    to the cyclic garbage collector.  If *owner* is ``NULL`` then no such
    association is made.  If *owner* is the same value as *obj* then any
    reference cycles involving *obj* can never be detected or broken by the
    cyclic garbage collector.  Responsibility for calling the C++ instance's
    destructor is always transfered to C++.


sipWrapper
----------

This is a C structure that represents a Python wrapped instance.  It is an
extension of the Python ``PyObject`` structure and so may be safely cast to
``PyObject``.  It includes a member called ``user`` which is of type
``PyObject *``.  This can be used for any purpose by handwritten code and will
automatically be garbage collected at the appropriate time.


sipWrapper_Check()
------------------

int sipWrapper_Check(PyObject \*obj)
    This returns a non-zero value if a Python object is a wrapped instance.
    *obj* is the Python object.


sipWrapperType
--------------

This is a C structure that represents a SIP generated type object.  It is an
extension of the Python ``PyTypeObject`` structure (which is itself an
extension of the Python ``PyObject`` structure) and so may be safely cast to
``PyTypeObject`` (and ``PyObject``).


Generated Type Convertors
-------------------------

These functions are deprecated from SIP v4.4.

SIP generates functions for all types being wrapped (including mapped types
defined with the `%MappedType`_ directive) that convert a Python object to the
C structure or C++ class instance.  The name of this convertor is the name of
the structure or class prefixed by ``sipForceConvertTo_``.

void \*sipForceConvertTo_*class*(PyObject \*obj, int \*iserr)
    *obj* is the Python object to convert.  If *obj* is ``NULL`` or the
    location pointed to by *iserr* is non-zero then the conversion is not
    attempted and ``NULL`` is returned.  If there was an error then the
    location pointed to by *iserr* is set to a non-zero value, a Python
    exception is raised, and ``NULL`` is returned.

SIP also generates functions for mapped types that convert a C structure or
C++ class instance to a Python object.  The name of this convertor is the name
of the structure or class prefixed by ``sipConvertFrom_``.

PyObject \*sipConvertFrom_*class*(void \*cppptr)
    *cppptr* is a pointer to the C structure or C++ class instance to convert.
    If there was an error then ``NULL`` is returned and a Python exception
    raised.

The convertor functions of all imported types are available to handwritten
code.


Generated Type Objects
----------------------

SIP generates a type object for each C structure or C++ class being wrapped.
These are sipWrapperType_ structures and are used extensively by the SIP API.

These objects are named with the structure or class name prefixed by
``sipClass_``.  For example, the type object for class ``Klass`` is
``sipClass_Klass``.

The type objects of all imported classes are available to handwritten code.


Generated Named Enum Type Objects
---------------------------------

SIP generates a type object for each named enum being wrapped.  These are
PyTypeObject structures.  (Anonymous enums are wrapped as Python integers.)

These objects are named with the fully qualified enum name (i.e. including any
enclosing scope) prefixed by ``sipEnum_``.  For example, the type object for
enum ``Enum`` defined in class ``Klass`` is ``sipEnum_Klass_Enum``.

The type objects of all imported named enums are available to handwritten code.


Generated Derived Classes
-------------------------

For most C++ classes being wrapped SIP generates a derived class with the same
name prefixed by ``sip``.  For example, the derived class for class ``Klass``
is ``sipKlass``.

If a C++ class doesn't have any virtual or protected methods in it or any of
it's super-class hierarchy, or does not emit any Qt signals, then a derived
class is not generated.

Most of the time handwritten code should ignore the derived classes.  The only
exception is that handwritten constructor code specified using the
`%MethodCode`_ directive should call the derived class's constructor (which
has the same C++ signature) rather then the wrapped class's constructor.


Generated Exception Objects
---------------------------

SIP generates a Python object for each exception defined with the `%Exception_`
directive.

These objects are named with the fully qualified exception name (i.e. including
any enclosing scope) prefixed by ``sipException_``.  For example, the type
object for enum ``Except`` defined in class ``Klass`` is
``sipException_Klass_Except``.

The objects of all imported exceptions are available to handwritten code.


Using the SIP Module in Applications
====================================

The main purpose of the SIP module is to provide functionality common to all
SIP generated bindings.  It is loaded automatically and most of the time you
will completely ignore it.  However, it does expose some functionality that can
be used by applications.

cast(obj, type)
    This does the Python equivalent of casting a C++ instance to one of its
    sub or super-class types.  *obj* is the Python object and *type* is the
    type.  A new Python object is returned that wraps the same C++ instance as
    *obj*, but has the type *type*.

delete(obj)
    For C++ instances this calls the C++ destructor.  For C structures it
    returns the structure's memory to the heap.  *obj* is the Python object.

isdeleted(obj)
    This returns True if the C++ instance or C structure has been destroyed or
    returned to the heap.  *obj* is the Python object.

setdeleted(obj)
    This marks the C++ instance or C structure as having been destroyed or
    returned to the heap so that future references to it raise an exception
    rather than cause a program crash.  Normally SIP handles such things
    automatically, but there are circumstances where this isn't possible.
    *obj* is the Python object.

settracemask(mask)
    If the bindings have been created with SIP's ``-r`` command line option
    then the generated code will produce debugging statements that trace the
    execution of the code.  (It is particularly useful when trying to
    understand the operation of a C++ library's virtual function calls.)

    Debugging statements are generated at the following points:

    - in a C++ virtual function (*mask* is ``0x0001``)
    - in a C++ constructor (*mask* is ``0x0002``)
    - in a C++ destructor (*mask* is ``0x0004``)
    - in a Python type's __init__ method (*mask* is ``0x0008``)
    - in a Python type's __del__ method (*mask* is ``0x0010``)
    - in a Python type's ordinary method (*mask* is ``0x0020``).

    By default the trace mask is zero and all debugging statements are
    disabled.

SIP_VERSION
    This is a Python integer object that represents the SIP version number as
    a 3 part hexadecimal number (e.g. v4.0.0 is represented as ``0x040000``).
    It was first implemented in SIP v4.2.

SIP_VERSION_STR
    This is a Python string object that defines the SIP version number as
    represented as a string.  For development snapshots it will start with
    ``snapshot-``.  It was first implemented in SIP v4.3.

transfer(obj, direction)
    This function is deprecated from SIP v4.3.  If *direction* is non-zero then
    the equivalent call is::

        sip.transferto(obj, None)

    If *direction* is zero then the equivalent call is::

        sip.transferback(obj)

transferback(obj)
    This function is a wrapper around `sipTransferBack()`_.

transferto(obj, owner)
    This function is a wrapper around `sipTransferTo()`_.

unwrapinstance(obj)
    Return the address, as a number, of the wrapped C/C++ structure or class
    instance *obj*.

voidptr
    This is the type object for the type SIP uses to represent a C/C++
    ``void *``.  The type constructor takes a single argument that must either
    be another ``voidptr``, ``None``, a Python CObject, or an integer.  The
    type has the following methods:

    __int__()
        This returns the pointer as an integer.

    __hex__()
        This returns the pointer as a hexadecimal string.

    ascobject()
        This returns the pointer as a Python CObject.

    asstring(nbytes)
        This returns a copy of the first *nbytes* of memory at the pointer as a
        Python string.

wrapinstance(addr, type)
    A C/C++ structure or class instance is wrapped and the Python object
    created is returned.  If the instance has already been wrapped then a new
    reference to the existing object is returned.  *addr* is the address of
    the instance represented as a number.  *type* is the type of the object
    (e.g. ``qt.QWidget``).

wrapper
    This is the type object of the base type of all instances wrapped by SIP.

wrappertype
    This is the type object of the metatype of the ``wrapper`` type.


The SIP Build System
====================

The purpose of the build system is to make it easy for you to write
configuration scripts in Python for your own bindings.  The build system takes
care of the details of particular combinations of platform and compiler.  It
supports over 50 different platform/compiler combinations.

The build system is implemented as a pure Python module called ``sipconfig``
that contains a number of classes and functions.  Using this module you can
write bespoke configuration scripts (e.g. PyQt's ``configure.py``) or use it
with other Python based build systems (e.g.
`Distutils <http://www.python.org/sigs/distutils-sig/distutils.html>`_ and
`SCons <http://www.scons.org>`_).

An important feature of SIP is the ability to generate bindings that are built
on top of existing bindings.  For example, both
`PyKDE <http://www.riverbankcomputing.co.uk/pykde/>`_ and
`PyQwt <http://pyqwt.sourceforge.net/>`_ are built on top of PyQt but all three
packages are maintained by different developers.  To make this easier PyQt
includes its own configuration module, ``pyqtconfig``, that contains additional
classes intended to be used by the configuration scripts of bindings built on
top of PyQt.  The SIP build system includes facilities that do a lot of the
work of creating these additional configuration modules.


``sipconfig`` Functions
-----------------------

create_config_module(module, template, content, macros=None)
    This creates a configuration module (e.g. ``pyqtconfig``) from a template
    file and a string.

    ``module`` is the name of the configuration module file to create.

    ``template`` is the name of the template file.

    ``content`` is a string which replaces every occurence of the pattern
    ``@SIP_CONFIGURATION@`` in the template file.  The content string is
    usually created from a Python dictionary using
    ``sipconfig.create_content()``.  ``content`` may also be a dictionary, in
    which case ``sipconfig.create_content()`` is automatically called to
    convert it to a string.

    ``macros`` is an optional dictionary of platform specific build macros.  It
    is only used if ``sipconfig.create_content()`` is called automatically to
    convert a ``content`` dictionary to a string.

create_content(dict, macros=None)
    This converts a Python dictionary to a string that can be parsed by the
    Python interpreter and converted back to an equivalent dictionary.  It is
    typically used to generate the content string for
    ``sipconfig.create_config_module()``.

    ``dict`` is the Python dictionary to convert.

    ``macros`` is the optional dictionary of platform specific build macros.

    Returns the dictionary as a string.

create_wrapper(script, wrapper, gui=0)
    This creates a platform dependent executable wrapper around a Python
    script.

    ``script`` is the full pathname of the script.

    ``wrapper`` is the pathname of the wrapper to create.

    ``gui`` is non-zero if a GUI enabled version of the interpreter should be
    used on platforms that require it.

    Returns the platform specific name of the wrapper.

error(msg)
    This displays an error message on ``stderr`` and calls ``sys.exit()`` with
    a value of 1.

    ``msg`` is the text of the message and should not include any newline
    characters.

format(msg, leftmargin=0, rightmargin=78)
    This formats a message by inserting newline characters at appropriate
    places.

    ``msg`` is the text of the message and should not include any newline
    characters.

    ``leftmargin`` is the optional position of the left margin.

    ``rightmargin`` is the optional position of the right margin.

inform(msg)
    This displays an information message on ``stdout``.

    ``msg`` is the text of the message and should not include any newline
    characters.

parse_build_macros(filename, names, overrides=None, properties=None)
    This parses a qmake compatible file of build system macros and converts it
    to a dictionary.  A macro is a name/value pair.  The dictionary is returned
    or None if any of the overrides was invalid.

    ``filename`` is the name of the file to parse.

    ``names`` is a list of the macro names to extract from the file.

    ``overrides`` is an optional list of macro names and values that modify
    those found in the file.  They are of the form *name=value* (in which case
    the value replaces the value found in the file) or *name+=value* (in which
    case the value is appended to the value found in the file).

    ``properties`` is an optional dictionary of property name and values that
    are used to resolve any expressions of the form ``$[name]`` in the file.

read_version(filename, description, numdefine=None, strdefine=None)
    This extracts version information for a package from a file, usually a C or
    C++ header file.  The version information must each be specified as a
    ``#define`` of a numeric (hexadecimal or decimal) value and/or a string
    value.

    ``filename`` is the name of the file to read.

    ``description`` is a descriptive name of the package used in error
    messages.

    ``numdefine`` is the optional name of the ``#define`` of the version as a
    number.  If it is ``None`` then the numeric version is ignored.

    ``strdefine`` is the optional name of the ``#define`` of the version as a
    string.  If it is ``None`` then the string version is ignored.

    Returns a tuple of the numeric and string versions.  ``sipconfig.error()``
    is called if either were required but could not be found.

version_to_sip_tag(version, tags, description)
    This converts a version number to a SIP version tag.  SIP uses the
    `%Timeline`_ directive to define the chronology of the different versions
    of the C/C++ library being wrapped.  Typically it is not necessary to
    define a version tag for every version of the library, but only for those
    versions that affect the library's API as SIP sees it.

    ``version`` is the numeric version number of the C/C++ library being
    wrapped.  If it is negative then the latest version is assumed.  (This is
    typically useful if a snapshot is indicated by a negative version number.)

    ``tags`` is the dictionary of SIP version tags keyed by the corresponding
    C/C++ library version number.  The tag used is the one with the smallest
    key (i.e. earliest version) that is greater than ``version``.

    ``description`` is a descriptive name of the C/C++ library used in error
    messages.

    Returns the SIP version tag.  ``sipconfig.error()`` is called if the C/C++
    library version number did not correspond to a SIP version tag.

version_to_string(v)
    This converts a 3 part version number encoded as a hexadecimal value to a
    string.

    ``v`` is the version number.

    Returns a string.


``sipconfig`` Classes
---------------------

Configuration
    This class encapsulates configuration values that can be accessed as
    instance objects.  A sub-class may provide a dictionary of additional
    configuration values in its constructor the elements of which will have
    precedence over the super-class's values.

    The following configuration values are provided:

        default_bin_dir
            The name of the directory where executables should be installed by
            default.

        default_mod_dir
            The name of the directory where SIP generated modules should be
            installed by default.

        default_sip_dir
            The name of the base directory where the ``.sip`` files for SIP
            generated modules should be installed by default.  A sub-directory
            with the same name as the module should be created and its ``.sip``
            files should be installed in the sub-directory.  The ``.sip``
            files only need to be installed if you might want to build other
            bindings based on them.

        platform
            The name of the platform/compiler for which the build system has
            been configured for.

        py_conf_inc_dir
            The name of the directory containing the ``pyconfig.h`` header
            file.

        py_inc_dir
            The name of the directory containing the ``Python.h`` header file.

        py_lib_dir
            The name of the directory containing the Python interpreter
            library.

        py_version
            The Python version as a 3 part hexadecimal number (e.g. v2.3.3 is
            represented as ``0x020303``).

        sip_bin
            The full pathname of the SIP executable.

        sip_config_args
            The command line passed to ``configure.py`` when SIP was
            configured.

        sip_inc_dir
            The name of the directory containing the ``sip.h`` header file.

        sip_mod_dir
            The name of the directory containing the SIP module.

        sip_version
            The SIP version as a 3 part hexadecimal number (e.g. v4.0.0 is
            represented as ``0x040000``).

        sip_version_str
            The SIP version as a string.  For development snapshots it will
            start with ``snapshot-``.

        universal
            The name of the MacOS/X SDK used when creating universal binaries.

    __init__(self, sub_cfg=None)
        Initialise the instance.

        ``sub_cfg`` is an optional list of sub-class configurations.  It should
        only be used by the ``__init__()`` method of a sub-class to append its
        own dictionary of configuration values before passing the list to its
        super-class.

    build_macros(self)
        Return the dictionary of platform specific build macros.

    set_build_macros(self, macros)
        Set the dictionary of platform specific build macros to be use when
        generating Makefiles.  Normally there is no need to change the default
        macros.

Makefile
    This class encapsulates a Makefile.  It is intended to be sub-classed to
    generate Makefiles for particular purposes.  It handles all platform and
    compiler specific flags, but allows them to be adjusted to suit the
    requirements of a particular module or program.  These are defined using a
    number of macros which can be accessed as instance objects.

    The following instance objects are provided to help in fine tuning the
    generated Makefile:

        chkdir
            A string that will check for the existence of a directory.

        config
            A reference to the ``configuration`` argument that was passed to
            the constructor.

        console
            A reference to the ``console`` argument that was passed to the
            constructor.

        copy
            A string that will copy a file.

        extra_cflags
            A list of additional flags passed to the C compiler.

        extra_cxxflags
            A list of additional flags passed to the C++ compiler.

        extra_defines
            A list of additional macro names passed to the C/C++ preprocessor.

        extra_include_dirs
            A list of additional include directories passed to the C/C++
            preprocessor.

        extra_lflags
            A list of additional flags passed to the linker.

        extra_lib_dirs
            A list of additional library directories passed to the linker.

        extra_libs
            A list of additional libraries passed to the linker.  The names of
            the libraries must be in platform neutral form (i.e. without any
            platform specific prefixes, version numbers or extensions).

        generator
            A string that defines the platform specific style of Makefile.  The
            only supported values are ``UNIX`` and something else that is not
            ``UNIX``.

        mkdir
            A string that will create a directory.

        rm
            A string that will remove a file.

    __init__(self, configuration, console=0, qt=0, opengl=0, python=0, threaded=0, warnings=None, debug=0, dir=None, makefile="Makefile", installs=None, universal='')
        Initialise the instance.

        ``configuration`` is the current configuration and is an instance of
        the ``Configuration`` class or a sub-class.

        ``console`` is set if the target is a console (rather than GUI) target.
        This only affects Windows and is ignored on other platforms.

        ``qt`` is set if the target uses Qt.  For Qt v4 a list of Qt libraries
        may be specified and a simple non-zero value implies QtCore and QtGui.

        ``opengl`` is set if the target uses OpenGL.

        ``python`` is set if the target uses Python.h.

        ``threaded`` is set if the target requires thread support.  It is set
        automatically if the target uses Qt and Qt has thread support enabled.

        ``warnings`` is set if compiler warning messages should be enabled.
        The default of ``None`` means that warnings are enabled for SIP v4.x
        and disabled for SIP v3.x.

        ``debug`` is set if debugging symbols should be generated.

        ``dir`` is the name of the directory where build files are read from
        and Makefiles are written to.  The default of ``None`` means the
        current directory is used.

        ``makefile`` is the name of the generated Makefile.

        ``installs`` is a list of extra install targets.  Each element is a two
        part list, the first of which is the source and the second is the
        destination.  If the source is another list then it is a list of source
        files and the destination is a directory.

        ``universal`` is the name of the SDK if universal binaries are to be
        created under MacOS/X.

    clean_build_file_objects(self, mfile, build)
        This generates the Makefile commands that will remove any files
        generated during the build of the default target.

        ``mfile`` is the Python file object of the Makefile.

        ``build`` is the dictionary created from parsing the build file.

    finalise(self)
        This is called just before the Makefile is generated to ensure that it
        is fully configured.  It must be reimplemented by a sub-class.

    generate(self)
        This generates the Makefile.

    generate_macros_and_rules(self, mfile)
        This is the default implementation of the Makefile macros and rules
        generation.

        ``mfile`` is the Python file object of the Makefile.

    generate_target_clean(self, mfile)
        This is the default implementation of the Makefile clean target
        generation.

        ``mfile`` is the Python file object of the Makefile.

    generate_target_default(self, mfile)
        This is the default implementation of the Makefile default target
        generation.

        ``mfile`` is the Python file object of the Makefile.

    generate_target_install(self, mfile)
        This is the default implementation of the Makefile install target
        generation.

        ``mfile`` is the Python file object of the Makefile.

    install_file(self, mfile, src, dst, strip=0)
        This generates the Makefile commands to install one or more files to a
        directory.

        ``mfile`` is the Python file object of the Makefile.

        ``src`` is the name of a single file to install or a list of a number
        of files to install.

        ``dst`` is the name of the destination directory.

        ``strip`` is set if the files should be stripped of unneeded symbols
        after having been installed.

    optional_list(self, name)
        This returns an optional Makefile macro as a list.

        ``name`` is the name of the macro.

        Returns the macro as a list.

    optional_string(self, name, default="")
        This returns an optional Makefile macro as a string.

        ``name`` is the name of the macro.

        ``default`` is the optional default value of the macro.

        Returns the macro as a string.

    parse_build_file(self, filename)
        This parses a build file (created with the ``-b`` SIP command line
        option) and converts it to a dictionary.  It can also validate an
        existing dictionary created through other means.

        ``filename`` is the name of the build file, or is a dictionary to be
        validated.  A valid dictionary will contain the name of the target to
        build (excluding any platform specific extension) keyed by ``target``;
        the names of all source files keyed by ``sources``; and, optionally,
        the names of all header files keyed by ``headers``.

        Returns a dictionary corresponding to the parsed build file.

    platform_lib(self, clib, framework=0)
        This converts a library name to a platform specific form.

        ``clib`` is the name of the library in cannonical form.

        ``framework`` is set if the library is implemented as a MacOS
        framework.

        Return the platform specific name.

    ready(self)
        This is called to ensure that the Makefile is fully configured.  It is
        normally called automatically when needed.

    required_string(self, name)
        This returns a required Makefile macro as a string.

        ``name`` is the name of the macro.

        Returns the macro as a string.  An exception is raised if the macro
        does not exist or has an empty value.

ModuleMakefile(Makefile)
    This class encapsulates a Makefile to build a generic Python extension
    module.

    __init__(self, configuration, build_file, install_dir=None, static=0, console=0, opengl=0, threaded=0, warnings=None, debug=0, dir=None, makefile="Makefile", installs=None, strip=1, export_all=0, universal='')
        Initialise the instance.

        ``configuration`` - see ``sipconfig.Makefile.__init__()``.

        ``build_file`` is the name of the build file.  Build files are
        generated using the ``-b`` SIP command line option.

        ``install_dir`` is the name of the directory where the module will be
        optionally installed.

        ``static`` is set if the module should be built as a static library
        (see `Builtin Modules and Custom Interpreters`_).

        ``console`` - see ``sipconfig.Makefile.__init__()``.

        ``qt`` - see ``sipconfig.Makefile.__init__()``.

        ``opengl`` - see ``sipconfig.Makefile.__init__()``.

        ``threaded`` - see ``sipconfig.Makefile.__init__()``.

        ``warnings`` - see ``sipconfig.Makefile.__init__()``.

        ``debug`` - see ``sipconfig.Makefile.__init__()``.

        ``dir`` - see ``sipconfig.Makefile.__init__()``.

        ``makefile`` - see ``sipconfig.Makefile.__init__()``.

        ``installs`` - see ``sipconfig.Makefile.__init__()``.

        ``strip`` is set if the module should be stripped of unneeded symbols
        after installation.  It is ignored if either ``debug`` or ``static`` is
        set, or if the platform doesn't support it.

        ``export_all`` is set if all of the module's symbols should be exported
        rather than just the module's initialisation function.  Exporting all
        symbols increases the size of the module and slows down module load
        times but may avoid problems with modules that use C++ exceptions.  All
        symbols are exported if either ``debug`` or ``static`` is set, or if
        the platform doesn't support it.

    finalise(self)
        This is a reimplementation of ``sipconfig.Makefile.finalise()``.

    generate_macros_and_rules(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_macros_and_rules()``.

    generate_target_clean(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_target_clean()``.

    generate_target_default(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_target_default()``.

    generate_target_install(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_target_install()``.

    module_as_lib(self, mname)
        This returns the name of a SIP v3.x module for when it is used as a
        library to be linked against.  An exception will be raised if it is
        used with SIP v4.x modules.

        ``mname`` is the name of the module.

        Returns the corresponding library name.

ParentMakefile(Makefile)
    This class encapsulates a Makefile that sits above a number of other
    Makefiles in sub-directories.

    __init__(self, configuration, subdirs, dir=None, makefile="Makefile", installs=None)
        Initialise the instance.

        ``configuration`` - see ``sipconfig.Makefile.__init__()``.

        ``subdirs`` is the sequence of sub-directories.

        ``dir`` - see ``sipconfig.Makefile.__init__()``.

        ``makefile`` - see ``sipconfig.Makefile.__init__()``.

        ``installs`` - see ``sipconfig.Makefile.__init__()``.

    generate_macros_and_rules(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_macros_and_rules()``.

    generate_target_clean(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_target_clean()``.

    generate_target_default(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_target_default()``.

    generate_target_install(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_target_install()``.

ProgramMakefile(Makefile)
    This class encapsulates a Makefile to build an executable program.

    __init__(self, configuration, build_file=None, install_dir=None, console=0, qt=0, opengl=0, python=0, threaded=0, warnings=None, debug=0, dir=None, makefile="Makefile", installs=None, universal='')
        Initialise the instance.

        ``configuration`` - see ``sipconfig.Makefile.__init__()``.

        ``build_file`` is the name of the optional build file.  Build files are
        generated using the ``-b`` SIP command line option.

        ``install_dir`` is the name of the directory where the executable
        program will be optionally installed.

        ``console`` - see ``sipconfig.Makefile.__init__()``.

        ``qt`` - see ``sipconfig.Makefile.__init__()``.

        ``opengl`` - see ``sipconfig.Makefile.__init__()``.

        ``python`` - see ``sipconfig.Makefile.__init__()``.

        ``threaded`` - see ``sipconfig.Makefile.__init__()``.

        ``warnings`` - see ``sipconfig.Makefile.__init__()``.

        ``debug`` - see ``sipconfig.Makefile.__init__()``.

        ``dir`` - see ``sipconfig.Makefile.__init__()``.

        ``makefile`` - see ``sipconfig.Makefile.__init__()``.

        ``installs`` - see ``sipconfig.Makefile.__init__()``.

    build_command(self, source)
        This creates a single command line that will create an executable
        program from a single source file.

        ``source`` is the name of the source file.

        Returns a tuple of the name of the executable that will be created and
        the command line.

    finalise(self)
        This is a reimplementation of ``sipconfig.Makefile.finalise()``.

    generate_macros_and_rules(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_macros_and_rules()``.

    generate_target_clean(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_target_clean()``.

    generate_target_default(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_target_default()``.

    generate_target_install(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_target_install()``.

PythonModuleMakefile(Makefile)
    This class encapsulates a Makefile that installs a pure Python module.

    __init__(self, configuration, dstdir, srcdir=None, dir=None, makefile="Makefile", installs=None)
        Initialise the instance.

        ``configuration`` - see ``sipconfig.Makefile.__init__()``.

        ``dstdir`` is the name of the directory in which the module's Python
        code will be installed.

        ``srcdir`` is the name of the directory (relative to ``dir``)
        containing the module's Python code.  It defaults to the same
        directory.

        ``dir`` - see ``sipconfig.Makefile.__init__()``.

        ``makefile`` - see ``sipconfig.Makefile.__init__()``.

        ``installs`` - see ``sipconfig.Makefile.__init__()``.

    generate_macros_and_rules(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_macros_and_rules()``.

    generate_target_install(self, mfile)
        This is a reimplementation of
        ``sipconfig.Makefile.generate_target_install()``.

SIPModuleMakefile(ModuleMakefile)
    This class encapsulates a Makefile to build a SIP generated Python
    extension module.

    finalise(self)
        This is a reimplementation of ``sipconfig.Makefile.finalise()``.


Building Your Extension with distutils
======================================

To build the example in `A Simple C++ Example`_ using distutils, it is
sufficient to create a standard ``setup.py``, listing ``word.sip`` among the
files to build, and hook-up SIP into distutils::

    from distutils.core import setup, Extension
    import sipdistutils

    setup(
      name = 'word',
      versione = '1.0',
      ext_modules=[
        Extension("word", ["word.sip", "word.cpp"]),
        ],

      cmdclass = {'build_ext': sipdistutils.build_ext}
    )

As we can see, the above is a normal distutils setup script, with just a
special line which is needed so that SIP can see and process ``word.sip``.
Then, running ``setup.py build`` will build our extension module.


Builtin Modules and Custom Interpreters
=======================================

Sometimes you want to create a custom Python interpreter with some modules
built in to the interpreter itself rather than being dynamically loaded.  To
do this the module must be created as a static library and linked with a
custom stub and the normal Python library.

To build the SIP module as a static library you must pass the ``-k`` command
line option to ``configure.py``.  You should then build and install SIP as
normal.  (Note that, because the module is now a static library, you will not
be able to import it.)

To build a module you have created for your own library you must modify your
own configuration script to pass a non-zero value as the ``static`` argument
of the ``__init__()`` method of the ``ModuleMakefile`` class (or any derived
class you have created).  Normally you would make this configurable using a
command line option in the same way that SIP's ``configure.py`` handles it.

The next stage is to create a custom stub and a Makefile.  The SIP distribution
contains a directory called ``custom`` which contains example stubs and a
Python script that will create a correct Makefile.  Note that, if your copy of
SIP was part of a standard Linux distribution, the ``custom`` directory may
not be installed on your system.

The ``custom`` directory contains the following files.  They are provided as
examples - each needs to be modified according to your particular
requirements.

    - ``mkcustom.py`` is a Python script that will create a Makefile which is
      then used to build the custom interpreter.  Comments in the file describe
      how it should be modified.

    - ``custom.c`` is a stub for a custom interpreter on Linux/UNIX.  It
      should also be used for a custom console interpreter on Windows (i.e.
      like ``python.exe``).  Comments in the file describe how it should be
      modified.

    - ``customw.c`` is a stub for a custom GUI interpreter on Windows (i.e.
      like ``pythonw.exe``).  Comments in the file describe how it should be
      modified.

Note that this technique does not restrict how the interpreter can be used.
For example, it still allows users to write their own applications that can
import your builtin modules.  If you want to prevent users from doing that,
perhaps to protect a proprietary API, then take a look at the
`VendorID <http://www.riverbankcomputing.co.uk/vendorid/>`__ package.