Chapter 1. Introduction
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## Chapter 1. Introduction

PyGTK 2.0 is a set of Python modules which provide a Python interface to GTK+ 2.X. Throughout the rest of this document PyGTK refers to the 2.X version of PyGTK and GTK and GTK+ refer to the 2.X version of GTK+. The primary web site for PyGTK is www.pygtk.org. The primary author of PyGTK is:

- James Henstridge james@daa.com.au

who is assisted by the developers listed in the AUTHORS file in the PyGTK distribution and the PyGTK community.

Python is an extensible, object-oriented interpreted programming language which is provided with a rich set of modules providing access to a large number of operating system services, internet services (such as HTML, XML, FTP, etc.), graphics (including OpenGL, TK, etc.), string handling functions, mail services (IMAP, SMTP, POP3, etc.), multimedia (audio, JPEG) and cryptographic services. In addition there are many other modules available from third parties providing many other services. Python is licensed under terms similar to the LGPL license and is available for Linux, Unix , Windows and Macintosh operating systems. More information on Python is available at www.python.org . The primary Author of Python is:

- Guido van Rossum guido@python.org

GTK (GIMP Toolkit) is a library for creating graphical user interfaces. It is licensed using the LGPL license, so you can develop open software, free software, or even commercial non-free software using GTK without having to spend anything for licenses or royalties.

It's called the GIMP toolkit because it was originally written for developing the GNU Image Manipulation Program (GIMP), but GTK has now been used in a large number of software projects, including the GNU Network Object Model Environment (GNOME) project. GTK is built on top of GDK (GIMP Drawing Kit) which is basically a wrapper around the low-level functions for accessing the underlying windowing functions (Xlib in the case of the X windows system). The primary authors of GTK are:

- Peter Mattis petm@xcf.berkeley.edu
- Spencer Kimball spencer@xcf.berkeley.edu
- Josh MacDonald jmacd@xcf.berkeley.edu

GTK is currently maintained by:

- Owen Taylor otaylor@redhat.com
- Tim Janik timj@gtk.org

GTK is essentially an object oriented application programmers interface (API). Although written completely in C, it is implemented using the idea of classes and callback functions (pointers to functions).

There is also a third component called GLib which contains a few replacements for some standard calls, as well as some additional functions for handling linked lists, etc. The replacement functions are used to increase GTK's portability, as some of the functions implemented here are not available or are nonstandard on other unixes such as `g_strerror`(). Some also contain enhancements to the libc versions, such as `g_malloc` that has enhanced debugging utilities.

In version 2.0, GLib has picked up the type system which forms the foundation for GTK's class hierarchy, the signal system which is used throughout GTK, a thread API which abstracts the different native thread APIs of the various platforms and a facility for loading modules.

As the last component, GTK uses the Pango library for internationalized text output.

This tutorial describes the Python interface to GTK+ and is based on the GTK+ 2.0 Tutorial written by Tony Gale and Ian Main. This tutorial attempts to document as much as possible of PyGTK, but is by no means complete.

This tutorial assumes some understanding of Python, and how to create and run Python programs. If you are not familiar with Python, please read the Python Tutorial first. This tutorial does not assume an understanding of GTK; if you are learning PyGTK to learn GTK, please comment on how you found this tutorial, and what you had trouble with. This tutorial does not describe how to compile or install Python, GTK+ or PyGTK.

This tutorial is based on:

- GTK+ 2.0 through GTK+ 2.4
- Python 2.2
- PyGTK 2.0 through PyGTK 2.4

The examples were written and tested on a RedHat 9.0 system.

This document is a "work in progress". Please look for updates on www.pygtk.org.

I would very much like to hear of any problems you have learning PyGTK from this document, and would appreciate input as to how it may be improved. Please see the section on Contributing for further information. If you encounter bugs please file a bug at bugzilla.gnome.org against the pygtk project. The information at www.pygtk.org about Bugzilla may help.

The PyGTK 2.0 Reference Manual is available at http://www.pygtk.org/pygtkreference. It describes in detail the PyGTK classes.

The PyGTK website (www.pygtk.org) contains other resources useful for learning about PyGTK including a link to the extensive FAQ and other articles and tutorials and an active maillist and IRC channel (see www.pygtk.org for details).

## 1.1. Exploring PyGTK

Johan Dahlin has written a small Python program (pygtkconsole.py) that runs on Linux and allows interactive exploration of PyGTK. The program provides a Python-like interactive interpreter interface that communicates with a child process that executes that entered commands. The PyGTK modules are loaded by default. A simple example session is:

      moe: 96:1095$ pygtkconsole.py
      Python 2.2.2, PyGTK 1.99.14 (Gtk+ 2.0.6)
      Interactive console to manipulate GTK+ widgets.
      >>> w=Window()
      >>> b=Button('Hello')
      >>> w.add(b)
      >>> def hello(b):
      ...     print "Hello, World!"
      ...
      >>> b.connect('clicked', hello)
      5
      >>> w.show_all()
      >>> Hello, World!
      Hello, World!
      Hello, World!

      >>> b.set_label("Hi There")
      >>>

This creates a window containing a button which prints a message ('Hello, World!') when clicked. This program makes it easy to try out various GTK widgets and PyGTK interfaces.

I also use a program that was developed by Brian McErlean as ActiveState recipe 65109 with some mods to make it run with PyGTK 2.X. I call it gpython.py. It works similar to the pygtkconsole.py program.

### Note

Both of these programs are known not to work on Microsoft Windows because they rely on Unix specific interfaces.

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