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<HTML>
<HEAD>
<TITLE>Types and Related Topics</TITLE>
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<TH COLSPAN="3" ALIGN="center">Python Bindings for KDE (PyKDE-3.16.0)</TH>
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<H1>Types and Related Topics</H1>
<H2>Static Member Functions</H2>
<P>
Static member functions are implemented as Python class functions.
For example the C++ static member function
<TT CLASS="LITERAL" >TQObject::connect()</TT>
is called from Python as
<TT CLASS="LITERAL">TQObject.connect()</TT> or
<TT CLASS="LITERAL">self.connect()</TT>
if called from a sub-class of
<TT CLASS="LITERAL">TQObject</TT>.
</P>
<h2>None and NULL</h2>
<P>Throughout the bindings, the
<TT CLASS="LITERAL">None</TT>
value can be specified wherever
<TT CLASS="LITERAL">NULL</TT>
is acceptable to the underlying C++ code.</P>
<P >Equally,
<TT CLASS="LITERAL">NULL</TT>
is converted to
<TT CLASS="LITERAL">None</TT>
whenever it is returned by the underlying C++ code
</P>
<h2>Enumerated Types</H2>
<P>
Enumerated types are implemented as a set of simple variables corresponding to
the separate enumerated values.
</P>
<P>
When using an enumerated value the name of the class (or a sub-class) in which
the enumerated type was defined in must be included. For example:
</P>
<TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%" >
<TR>
<TD>
<PRE CLASS="PROGRAMLISTING">
TQt.SolidPattern
TQWidget.TabFocus
TQFrame.TabFocus
</PRE>
</TD>
</TR>
</TABLE>
<H2>Namespaces</H2>
<P>
The C++ code in KDE makes extensive use of namespaces (especially in the tdeio, kjs,
tdehtml, tdefile, and tdeparts modules). In PyKDE, namespaces are treated as a "superclass".
For example, "from tdeparts import KParts" will import the KParts namespace and all
its members. To reference a class in the namespace, use <namespace name>..<classname>,
for example, KParts.ReadOnlyPart. It isn't necessary to import the <classname> (ReadOnlyPart
in the example).
</P>
<h2>Return and Argument Types</h2>
<p>
Some return types or argument types may be different than those in the C++ KDE libs. This is
done for convenience (eg returning/taking Python lists or dicts), because arguments are
scalar (non-object) types passed by reference (eg int*, bool&), or because there is no
way to express the C++ type in Python (eg template types)
</p>
<p>
Please check the <a href="docs.html">Class Reference Docs</a> which list all classes
and methods in Python format.
</p>
<h2>Version Information</h2><h4><i>New in PyKDE-3.11</i></h4>
<p>
PyKDE provides methods for determining both the KDE version being run and the PyKDE
version being run. The version methods are:
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<th align = "left" width = "20%"><u>return type</u></th>
<th align = "left" width = "20%"><u>KDE</u></th>
<th align = "center" width = "10%"><u>Example</u></th>
<th></th>
<th align = "left" width = "20%"><u>PyKDE</u></th>
<th align = "center" width = "20%"><u>Example</u></th>
</tr>
<tr>
<td>int</td>
<td>KDE.versionMajor ()</td>
<td align = "center">3</td>
<td></td>
<td>PyKDE.versionMajor ()</td>
<td align = "center">3</td>
</tr>
<tr>
<td>int</td>
<td>KDE.versionMinor ()</td>
<td align = "center">1</td>
<td></td>
<td>PyKDE.versionMinor ()</td>
<td align = "center">8</td>
</tr>
<tr>
<td>int</td>
<td>KDE.versionRelease ()</td>
<td align = "center">4</td>
<td></td>
<td>PyKDE.versionRelease ()</td>
<td align = "center">0</td>
</tr>
<tr>
<td>string</td>
<td>KDE.versionString ()</td>
<td align = "center">"3.1.4"</td>
<td></td>
<td>PyKDE.versionString ()</td>
<td align = "center">"3.11.0"</td>
</tr>
</table>
<h2>Abstract Classes and Pure Virtual Methods</h2>
<P>
C++ allows the use of abstract classes. Abstract classes cannot be used in programs
(instantiated) directly; their only purpose is to serve as a base class from which
programmers can derive other classes that can be used.
</P>
<P>
An abstract class in C++ is defined as a class that has one or more 'pure virtual'
methods. These can be identified in the C++ header files or C++ docs as methods set
equal to 0, for example:
</P>
<TABLE BORDER="0" BGCOLOR="#E0E0E0" WIDTH="100%">
<TR>
<TD>
<PRE CLASS="PROGRAMLISTING">
virtual int somePureVirtualMethod (int a) = 0;
</PRE>
</TD>
</TR>
</TABLE>
<P>
To derive a useful class from the abstract class, the programmer has to write methods
to overload each of the pure virtual methods. Following a suggestion on the mailing
list, the docs attempt to flag all abstract classes and identify the pure virtual
methods which must be overloaded in the derived class. Derived classes can be created
in Python by writing Python methods to overload the pure virtual methods - no C++ code
is required.
</P>
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