
Graphic User Interface FAQ
**************************


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


What platform-independent GUI toolkits exist for Python?
========================================================

Depending on what platform(s) you are aiming at, there are several.
Some of them haven't been ported to Python 3 yet.  At least Tkinter
and Qt are known to be Python 3-compatible.


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 (since it comes included with most binary distributions of
Python) and use. For more info about Tk, including pointers to the
source, see the Tcl/Tk home page.  Tcl/Tk is fully portable to the Mac
OS X, Windows, and Unix platforms.


wxWidgets
---------

wxWidgets (http://www.wxwidgets.org) is a free, portable GUI class
library written in C++ that provides a native look and feel on a
number of platforms, with Windows, Mac OS X, GTK, X11, all listed as
current stable targets.  Language bindings are available for a number
of languages including Python, Perl, Ruby, etc.

wxPython (http://www.wxpython.org) is the Python binding for
wxwidgets.  While it often lags slightly behind the official wxWidgets
releases, it also offers a number of features via pure Python
extensions that are not available in other language bindings.  There
is an active wxPython user and developer community.

Both wxWidgets and wxPython are free, open source, software with
permissive licences that allow their use in commercial products as
well as in freeware or shareware.


Qt
--

There are bindings available for the Qt toolkit (using either PyQt or
PySide) and for KDE (PyKDE). PyQt is currently more mature than
PySide, but you must buy a PyQt license from Riverbank Computing if
you want to write proprietary applications.  PySide is free for all
applications.

Qt 4.5 upwards is licensed under the LGPL license; also, commercial
licenses are available from The Qt Company.


Gtk+
----

The GObject introspection bindings for Python allow you to write GTK+
3 applications.  There is also a Python GTK+ 3 Tutorial.

The older PyGtk bindings for the Gtk+ 2 toolkit have been implemented
by James Henstridge; see <http://www.pygtk.org>.


FLTK
----

Python bindings for the FLTK toolkit, a simple yet powerful and mature
cross-platform windowing system, are available from the PyFLTK
project.


FOX
---

A wrapper for the FOX toolkit called FXpy is available.  FOX supports
both Unix variants and Windows.


OpenGL
------

For OpenGL bindings, see PyOpenGL.


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

By installing the PyObjc Objective-C bridge, Python programs can use
Mac OS X's Cocoa libraries.

*Pythonwin* by Mark Hammond includes an interface to the Microsoft
Foundation Classes and a Python programming environment that's written
mostly in Python using the MFC classes.


Tkinter questions
=================


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.sourceforge.net/).

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).
