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  <chapter id="pygtk-introduction">
  <title>Introduction</title>

  <para>This document describes most of the <literal>PyGTK</literal> version
  2.0 through 2.24 classes and their methods and associated
  functions. Deprecated classes, functions and methods have been
  specifically left out of this reference though classes that have become
  deprecated since PyGTK 2.0 have been left in but annotated with a
  deprecation warning. This document attempts to document as much of the
  <literal>PyGTK</literal> <literal>API</literal> as possible but there are
  undoubtedly errors and omissions. If you discover any of these please file
  a bug report at <ulink
  url="http://bugzilla.gnome.org">bugzilla.gnome.org</ulink> for the
  <literal>pygtk</literal> project. Specific areas that have not been
  documented include:</para>

  <itemizedlist>
    <listitem>
      <simpara>The Cairo classes</simpara>
    </listitem>
  </itemizedlist>

  <para>This reference describes the API for <literal>PyGTK</literal> as of
  version 2.24. The differences in the API between version 2.24 and previous
  versions are denoted in this reference with a Note that describes the
  availability of the object, constructor, method or function. Any of these
  that do not have a notation can be assumed to be available in all versions
  of PyGTK from 2.0 and up. In the case of properties and signals the
  availability is dependent on the version of the underlying GTK+, GDK or Pango
  libraries. These will be annotated appropriately in a similar fashion. The
  source code must be consulted if this reference and your version of
  <literal>PyGTK</literal> seem to differ. You are encouraged to use the latest
  version of <literal>PyGTK</literal> that is available. See the <ulink
  url="http://www.pygtk.org"><literal>PyGTK</literal> homepage</ulink> for
  more information and more resources on how to use PyGTK as well as help in
  its development.</para>

  <para> The Reference contains a chapter for each <literal>PyGTK</literal>
  module (that corresponds to the underlying <literal>GTK+</literal>
  library) containing the class descriptions. The second chapter illustrates
  the <literal>PyGTK</literal> class hierarchy covering the gobject, gtk,
  gtk.gdk and pango modules.</para>

  <para>The class descriptions are arranged alphabetically within the
  chapters. Currently there are five module chapters:</para>

  <variablelist>
    <varlistentry>
      <term>The&nbsp;<literal>atk</literal>&nbsp;module</term>
      <listitem><simpara>The classes that are included in the
      <literal>atk</literal> module of <literal>PyGTK</literal> and are
      accessed similar to: atk.Object. These classes are the base object
      classes that provide accessibility support for the
      <literal>gtk</literal> module classes.</simpara>
      </listitem>
    </varlistentry>
    <varlistentry>
      <term>The&nbsp;<literal>gtk</literal>&nbsp;module</term>
      <listitem><simpara>The classes that are included in the
      <literal>gtk</literal> module of <literal>PyGTK</literal> and are
      accessed similar to: gtk.Widget. These classes are the "higher" level
      widget classes that provide most of the user interface widgets used
      for application development.</simpara>
      </listitem>
    </varlistentry>
    <varlistentry>
      <term>The&nbsp;<literal>gtk.gdk</literal>&nbsp;module</term>
      <listitem><simpara>The classes that are included in the
      <literal>gtk.gdk</literal> module of <literal>PyGTK</literal>. These
      classes are "lower" level classes that provide more fundamental
      capabilities that the <literal>gtk</literal> module widgets are built
      upon. These classes provide an abstract interface to the underlying
      window system (either X Window System or Microsoft Windows).</simpara>
      </listitem>
    </varlistentry>
    <varlistentry>
        <term>The&nbsp;<literal>gtk.glade</literal>&nbsp;module</term>
      <listitem><simpara>The classes that are included in the
      <literal>gtk.glade</literal> module of <literal>PyGTK</literal>. These
      classes provide access to the libglade functions that allow the
      dynamic loading of user interfaces from XML descriptions.</simpara>
      </listitem>
    </varlistentry>
    <varlistentry>
      <term>The&nbsp;<literal>pango</literal>&nbsp;module</term>
      <listitem>
	<simpara>The classes that are included in the
	<literal>pango</literal> module of <literal>PyGTK</literal>. These
	classes provide access to the Pango text layout and rendering
	engines. PyGTK supports a subset of the full Pango capability:
	mainly the high level layout capabilities exposed by the
	pango.Layout objects. The low level rendering capabilities have not
	been exposed mostly because there isn't a full GObject interface to
	the underlying Pango data structures. It's also likely that the
	rendering capabilities require more performance that Python can
	provide.</simpara>
      </listitem>
    </varlistentry>
  </variablelist>

  <para>The <literal>gobject</literal> module is documented in the <link
  linkend="pygobject-reference">PyGObject Reference Manual</link>.</para>

  <sect1 id="pygtk-reference-format">
    <title>Reference Page Format</title>

    <para>Each <literal>PyGTK</literal> class is described in a reference
page that has a number of sections in a fixed format. Each reference page
will have a subset of the following sections:</para>

    <variablelist>
      <varlistentry>
	<term>Name</term>
	<listitem>
	  <simpara>The name and a one-line description of the
class.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Synopsis</term>
	<listitem>
	  <simpara>A synopsis of the class and its methods and
optionally a list of associated functions.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Ancestry</term>
	<listitem>
	  <simpara>The list of the parent classes of the class. This
section may not be present in all class descriptions.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Properties</term>
 	<listitem>
	  <simpara>A list of the properties (internal state)
supported by the class. This section may not be present in all classes. The
property descriptions include the name, the access operations (e.g. Read,
Write), and a brief description. Properties are accessed using the <link
linkend="method-gobject--set-property"><methodname>gobject.set_property</methodname>()</link> 
and <link
linkend="method-gobject--get-property"><methodname>gobject.get_property</methodname>()</link> 
methods that are available to every <literal>PyGTK</literal> object. This
section may not be present in all class descriptions.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Style&nbsp;Properties</term>
	<listitem>
	  <simpara>A list of style properties supported by the
class. Similar to the properties (described above) the style properties hold
information about the style of a widgets e.g. border style, shadow type,
etc. Most widgets do not support style properties so this section is not
present in most class descriptions. Only PyGTK 2.4 has the ability to access
style properties.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Child&nbsp;Properties</term>
	<listitem>
	  <simpara>A list of child properties supported by the
class. Similar to the properties (described above) the child properties hold
information about the properties of a widget's child widget. Only container
widgets support child properties so this section is not present in most
class descriptions.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Attributes</term>
	<listitem>
	  <simpara>A set of internal object state data accessible as
Python attributes (e.g. object.attr). The attribute descriptions include a
name by which the attribute data is accessed, the access mode (e.g. Read,
Write), and a brief description of the attribute. Most
<literal>PyGTK</literal> classes do not support attributes so this section
is not present in most class descriptions.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Signal&nbsp;Prototypes</term>
	<listitem>
	  <simpara>A list of the signals supported by the class
including the signal name and a synopsis of the signal handler function
prototype. This section may not be present in all class descriptions; most
<literal>gtk.gdk</literal> classes do not support signals.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Description</term>
	<listitem><simpara>A description of the class and possibly some of
the methods supported by the class.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Constructor</term>
	<listitem>
	  <simpara>The description of the class object constructor
including the synopsis with brief parameter descriptions and a description
of th use of the constructor. There may be more than one constructor
description if the constructor supports different parameter lists. This
section may not be present in all class descriptions.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Methods</term>
	<listitem>
	  <simpara>A list of methods supported by the class. Each
method description includes: a synopsis of the method and its parameters as
well as a brief description of each parameter and return value (if any);
and, a description of the use of the method.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Functions</term>
	<listitem>
	  <simpara>A list of related functions. Each function
description includes a synopsis of the function and its parameters and
return value (if any), and a description of the use of the
function.</simpara>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>Signals</term>
	<listitem>
	  <simpara>A list of signals including a synopsis of the
signal handler prototype function with its parameters and return value (if
any). The signal emission conditions are briefly described. This section is
not present in all class descriptions; specifically, the
<literal>gtk.gdk</literal> classes do not usually support signals.</simpara>
	</listitem>
      </varlistentry>
    </variablelist>

    <para>The function and method synopsis parameters are displayed in
<emphasis role="bold">bold</emphasis> to denote Python keyword parameters.
Also if the parameter is optional its default value will be displayed. For
example the <link linkend="constructor-gtkbutton">gtk.Button</link>()
constructor synopsis is:</para>

    <programlisting>
<constructorsynopsis language="python">
	<methodname><link
linkend="constructor-gtkbutton">gtk.Button</link></methodname>
	<methodparam><parameter
		       role="keyword">label</parameter><initializer>None</initializer></methodparam>
	<methodparam><parameter
		       role="keyword">stock</parameter><initializer>None</initializer></methodparam>
      </constructorsynopsis>
</programlisting>

    <para>The parameters <parameter>label</parameter> and
<parameter>stock</parameter> are keyword parameters that can be specified in
a call either by position or keyword (in which case position is not
important). The following calls have the same result:</para>

    <programlisting>
  b = gtk.Button("Cancel")
  b = gtk.Button(label="Cancel")
  b = gtk.Button("Cancel", None)
  b = gtk.Button("Cancel", stock=None)
  b = gtk.Button(stock=None, label="Cancel")
</programlisting>

    <para>Parameters that are not keyword parameters are displayed in
    <emphasis>italic</emphasis> and must be specified positionally but may
    also be optional.</para>

  </sect1>

  </chapter>