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diff --git a/doc/limits.html b/doc/limits.html new file mode 100644 index 0000000..3316c8c --- /dev/null +++ b/doc/limits.html @@ -0,0 +1,427 @@ +<HTML +><HEAD +><TITLE +>General Limitations</TITLE +><META +NAME="GENERATOR" +CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK +REL="HOME" +TITLE="Python Bindings for KDE (PyKDE-3.16.0)" +HREF="index.html"><LINK +REL="PREVIOUS" +TITLE="Python Bindings for KDE (PyKDE-3.16.0)" +HREF="index.html"><LINK +REL="NEXT" +TITLE="Signal and Slot Support" +HREF="signal.html"></HEAD +><BODY +CLASS="SECT1" +><DIV +CLASS="NAVHEADER" +><TABLE +SUMMARY="Header navigation table" +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TH +COLSPAN="3" +ALIGN="center" +>Python Bindings for KDE (PyKDE-3.3.16.0)</TH +></TR +><TR +><TD +WIDTH="10%" +ALIGN="left" +VALIGN="bottom" +><A +HREF="dcopext.html" +ACCESSKEY="P" +>Prev</A +></TD +><TD +WIDTH="80%" +ALIGN="center" +VALIGN="bottom" +></TD +><TD +WIDTH="10%" +ALIGN="right" +VALIGN="bottom" +><A +HREF="signal.html" +ACCESSKEY="N" +>Next</A +></TD +></TR +></TABLE +><HR +ALIGN="LEFT" +WIDTH="100%"></DIV +><DIV +CLASS="SECT1" +><H1 +CLASS="SECT1" +><A +NAME="AEN28" +></A +>General Limitations</H1 +><DIV +CLASS="SECT2" +><H2 +CLASS="SECT2" +><A +NAME="AEN30" +></A +>Python Strings, Qt Strings and Unicode</H2 +><P +>Unicode support was added to Qt in v2.0 and to Python in v1.6. In Qt, Unicode +support is implemented using the <TT +CLASS="LITERAL" +>QString</TT +> class. It is +important to understand that <TT +CLASS="LITERAL" +>QString</TT +>s, Python string objects +and Python Unicode objects are all different but conversions between them are +automatic in many cases and easy to achieve manually when needed.</P +><P +>Whenever PyKDE expects a <TT +CLASS="LITERAL" +>QString</TT +> as a function argument, a +Python string object or a Python Unicode object can be provided instead, and +PyKDE will do the necessary conversion automatically.</P +><P +>You may also manually convert Python string and Unicode objects to +<TT +CLASS="LITERAL" +>QString</TT +>s by using the <TT +CLASS="LITERAL" +>QString</TT +> constructor +as demonstrated in the following code fragment.</P +><TABLE +BORDER="0" +BGCOLOR="#E0E0E0" +WIDTH="100%" +><TR +><TD +><PRE +CLASS="PROGRAMLISTING" +>qs1 = QString('Converted Python string object') +qs2 = QString(u'Converted Python Unicode object')</PRE +></TD +></TR +></TABLE +><P +>In order to convert a <TT +CLASS="LITERAL" +>QString</TT +> to a Python string object use +the Python <TT +CLASS="LITERAL" +>str()</TT +> function. Applying +<TT +CLASS="LITERAL" +>str()</TT +> to a null <TT +CLASS="LITERAL" +>QString</TT +> and an empty +<TT +CLASS="LITERAL" +>QString</TT +> both result in an empty Python string object.</P +><P +>In order to convert a <TT +CLASS="LITERAL" +>QString</TT +> to a Python Unicode object use +the Python <TT +CLASS="LITERAL" +>unicode()</TT +> function. Applying +<TT +CLASS="LITERAL" +>unicode()</TT +> to a null <TT +CLASS="LITERAL" +>QString</TT +> and an empty +<TT +CLASS="LITERAL" +>QString</TT +> both result in an empty Python Unicode object.</P +></DIV +><DIV +CLASS="SECT2" +><H2 +CLASS="SECT2" +><A +NAME="AEN53" +></A +>Access to Protected Member Functions</H2 +><P +>When an instance of a C++ class is not created from Python it is not possible +to access the protected member functions, or emit the signals, of that +instance. Attempts to do so will raise a Python exception. Also, any Python +methods corresponding to the instance's virtual member functions will never be +called.</P +></DIV +><DIV +CLASS="SECT2" +><H2 +CLASS="SECT2" +><A +NAME="AEN56" +></A +>Garbage Collection</H2 +><P +>C++ does not garbage collect unreferenced class instances, whereas Python does. +In the following C++ fragment both colours exist even though the first can no +longer be referenced from within the program:</P +><TABLE +BORDER="0" +BGCOLOR="#E0E0E0" +WIDTH="100%" +><TR +><TD +><PRE +CLASS="PROGRAMLISTING" +>c = QColor(); +c = QColor();</PRE +></TD +></TR +></TABLE +><P +>In the corresponding Python fragment, the first colour is destroyed when +the second is assigned to <TT +CLASS="LITERAL" +>c</TT +>:</P +><TABLE +BORDER="0" +BGCOLOR="#E0E0E0" +WIDTH="100%" +><TR +><TD +><PRE +CLASS="PROGRAMLISTING" +>c = QColor() +c = QColor()</PRE +></TD +></TR +></TABLE +><P +>In Python, each colour must be assigned to different names. Typically this +is done within class definitions, so the code fragment would be something like:</P +><TABLE +BORDER="0" +BGCOLOR="#E0E0E0" +WIDTH="100%" +><TR +><TD +><PRE +CLASS="PROGRAMLISTING" +>self.c1 = QColor() +self.c2 = QColor()</PRE +></TD +></TR +></TABLE +><P +>Sometimes a Qt class instance will maintain a pointer to another instance and +will eventually call the destructor of that second instance. The most common +example is that a <TT +CLASS="LITERAL" +>QObject</TT +> (and any of its sub-classes) keeps +pointers to its children and will automatically call their destructors. In +these cases, the corresponding Python object will also keep a reference to the +corresponding child objects.</P +><P +>So, in the following Python fragment, the first <TT +CLASS="LITERAL" +>QLabel</TT +> is +not destroyed when the second is assigned to <TT +CLASS="LITERAL" +>l</TT +> because the +parent <TT +CLASS="LITERAL" +>QWidget</TT +> still has a reference to it.</P +><TABLE +BORDER="0" +BGCOLOR="#E0E0E0" +WIDTH="100%" +><TR +><TD +><PRE +CLASS="PROGRAMLISTING" +>p = QWidget() +l = QLabel('First label',p) +l = QLabel('Second label',p)</PRE +></TD +></TR +></TABLE +></DIV +><DIV +CLASS="SECT2" +><H2 +CLASS="SECT2" +><A +NAME="AEN72" +></A +>C++ Variables</H2 +><P +>Access to C++ variables is supported. They are accessed as Python instance +variables. For example:</P +><TABLE +BORDER="0" +BGCOLOR="#E0E0E0" +WIDTH="100%" +><TR +><TD +><PRE +CLASS="PROGRAMLISTING" +>tab = QTab() +tab.label = "First Tab" +tab.r = QRect(10,10,75,30)</PRE +></TD +></TR +></TABLE +><P +>Global variables and static class variables are effectively read-only. They +can be assigned to, but the underlying C++ variable will not be changed. This +may change in the future.</P +><P +>Access to protected C++ class variables is not supported. This may change in +the future.</P +></DIV +><DIV +CLASS="SECT2" +><H2 +CLASS="SECT2" +><A +NAME="AEN78" +></A +>Multiple Inheritance</H2 +><P +>It is not possible to define a new Python class that sub-classes from more than +one Qt class.</P +></DIV +></DIV> + +<H2 CLASS="SECT2">tr() methods</H2> +<P> +In a normal Qt installation, every descendant of QObject inherits two methods +(tr (const char *) and tr (const char *, const char *) from QObject explicitly +and also overloads these methods via the moc mechanism (by defining Q_OBJECT +in the class declaration). KDE however is compiled with -DQT_NO_TRANSLATION, +which prevents moc from creating the overloading tr() methods, and also produces +side-effects with a normal Qt installation which was compiled without the +-DQT_NO_TRANSLATION switch. +</P> +<P> +PyKDE handles this situation by NOT providing tr() methods (either the inherited +methods from QObject or the moc generated methods) for any KDE based QObject +descendant. The tr() methods are static, so QObject::tr () methods are available +via PyQt, as are tr() methods for any PyQt QObject descendant. PyKDE's handling +of these methods has no effect on PyQt. +</P> +<P>Instead of the tr() methods, KDE uses corresponding i18n() methods for translating. +These methods are available in the kdecore module of PyKDE. For compatibility with +KDE, you should use the i18n methods. +</P> +<H2>Socket classes</H2> +<P> +The following classes (introduced in KDE2.2.0) are NOT yet implemented: +</P> +<TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%"> +<TR> +<TD> +<PRE CLASS="PROGRAMLISTING"> +KAddressInfo +KExtendedSocket +KInetSocketAddress +KSocketAddress +KUnixSocketAddress +KSocks +</PRE> +</TD> +</TR> +</TABLE> +<P> +Most of their functionality already exists in the Python socket class or in the +KSocket class (kdecore module). These classes may be implemented at a future date +(they require support for C socket structures and careful handling to avoid buffer +overflow problems/exploits) +</P> + +<DIV +CLASS="NAVFOOTER" +><HR +ALIGN="LEFT" +WIDTH="100%"><TABLE +SUMMARY="Footer navigation table" +WIDTH="100%" +BORDER="0" +CELLPADDING="0" +CELLSPACING="0" +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +><A +HREF="dcopext.html" +ACCESSKEY="P" +>Prev</A +></TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +><A +HREF="index.html" +ACCESSKEY="H" +>Home</A +></TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +><A +HREF="signal.html" +ACCESSKEY="N" +>Next</A +></TD +></TR +><TR +><TD +WIDTH="33%" +ALIGN="left" +VALIGN="top" +>DCOP and Extensions</TD +><TD +WIDTH="34%" +ALIGN="center" +VALIGN="top" +> </TD +><TD +WIDTH="33%" +ALIGN="right" +VALIGN="top" +>Signal and Slot Support</TD +></TR +></TABLE +></DIV +></BODY +></HTML +> |