GUI FAQ

[amk@nyman.amk.ca]

The GUI FAQ is really minimal; there weren't many questions in the old
FAQ about GUIs, so this FAQ consists of two general questions about
what GUI toolkit are available from Python, and two very specific
Tkinter questions.

--amk

Title: Graphic User Interface FAQ
Content-type: text/x-rst

====================================
Graphic User Interface FAQ
====================================

:Date: $Date: 2003/08/15 21:14:43 $
:Version: $Revision: 1.2 $
:Web site: http://www.python.org/

.. contents::
.. sectnum::

General GUI Questions
============================

What platform-independent GUI toolkits exist for Python?
----------------------------------------------------------------
Depending on what platform(s) you are aiming at, there are several.

Tkinter
''''''''''''

Standard builds of Python include an object-oriented interface to the
Tcl/Tk widget set, called Tkinter.  This is probably the easiest to
install and use.  For more info about Tk, including pointers to the
source, see the Tcl/Tk home page at http://www.tcl.tk.  Tcl/Tk is
fully portable to the MacOS, Windows, and Unix platforms.

wxWindows
'''''''''''''


wxWindows is a portable GUI class library written in C++ that's a
portable interface to various platform-specific libraries; wxPython is
a Python interface to wxWindows.  wxWindows supports Windows and MacOS;
on Unix variants, it supports both GTk+ and Motif toolkits.
wxWindows preserves the look and feel of the underlying graphics
toolkit, and there is quite a rich widget set and collection of GDI
classes.  See `the wxWindows page <http://www.wxwindows.org>`_ for more
details.  

`wxPython <http://alldunn.com/wxPython>`_ is an extension module that
wraps many of the wxWindows C++ classes, and is quickly gaining
popularity amongst Python developers.  You can get wxPython as part of
the source or CVS distribution of wxWindows, or directly from its home
page.

GTk+
'''''''''''

PyGTk bindings for the GTk+ Toolkit by James Henstridge are available;
see ftp://ftp.daa.com.au/pub/james/python.  

Qt
''''''

There are bindings available for the Qt toolkit (PyQt). and for KDE
(PyKDE); see http://www.thekompany.com/projects/pykde.  If you're writing 
open source software, you don't need to pay for PyQt, but if you want to write
proprietary applications, you must buy a license from XXX.

For OpenGL bindings, see `PyOpenGL <http://pyopengl.sourceforge.net>`_.


What platform-specific GUI toolkits exist for Python?
----------------------------------------------------------------

`The Mac port <http://www.python.org/download/download_mac.html>`_ by
Jack Jansen has a rich and ever-growing set of modules that support
the native Mac toolbox calls.  The port includes support for MacOS9
and MacOS X's Carbon libraries.  By installing the `PyObjc Objective-C
bridge <http://pyobjc.sourceforge.net>`_, Python programs can use
MacOS X's Cocoa libraries. See the documentation that comes with the
Mac port.

`Pythonwin <http://www.python.org/windows>`_ by Mark Hammond 
includes an interface to the Microsoft Foundation
Classes and a Python programming environment using it that's written
mostly in Python.  

Tkinter
=====================

How do I freeze Tkinter applications?
---------------------------------------------

Freeze is a tool to create stand-alone applications.  When freezing
Tkinter applications, the applications will not be truly stand-alone,
as the application will still need the Tcl and Tk libraries.

One solution is to ship the application with the tcl and tk libraries,
and point to them at run-time using the TCL_LIBRARY and TK_LIBRARY
environment variables.

To get truly stand-alone applications, the Tcl scripts that form
the library have to be integrated into the application as well. One
tool supporting that is SAM (stand-alone modules), which is part
of the Tix distribution (http://tix.mne.com). Build Tix with SAM 
enabled, perform the appropriate call to Tclsam_init etc inside 
Python's Modules/tkappinit.c, and link with libtclsam
and libtksam (you might include the Tix libraries as well).


Can I have Tk events handled while waiting for I/O?
-----------------------------------------------------------
Yes, and you don't even need threads!  But you'll have to
restructure your I/O code a bit.  Tk has the equivalent of Xt's
XtAddInput() call, which allows you to register a callback function
which will be called from the Tk mainloop when I/O is possible on a
file descriptor.  Here's what you need::

        from Tkinter import tkinter
        tkinter.createfilehandler(file, mask, callback)

The file may be a Python file or socket object (actually, anything
with a fileno() method), or an integer file descriptor.  The mask is
one of the constants tkinter.READABLE or tkinter.WRITABLE.  The
callback is called as follows::

        callback(file, mask)

You must unregister the callback when you're done, using ::

        tkinter.deletefilehandler(file)

Note: since you don't know *how many bytes* are available for reading,
you can't use the Python file object's read or readline methods, since
these will insist on reading a predefined number of bytes.  For
sockets, the recv() or recvfrom() methods will work fine; for other
files, use os.read(file.fileno(), maxbytecount).


I can't get key bindings to work in Tkinter: why?
---------------------------------------------------
An often-heard complaint is that event handlers bound to events
with the bind() method don't get handled even when the appropriate
key is pressed.

The most common cause is that the widget to which the binding applies
doesn't have "keyboard focus".  Check out the Tk documentation
for the focus command.  Usually a widget is given the keyboard
focus by clicking in it (but not for labels; see the takefocus
option).