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# Graphic User Interface FAQ

Contents

- Graphic User Interface FAQ
  - General GUI Questions
    - What platform-independent GUI toolkits exist for Python?
      - Tkinter
      - wxWindows
      - Qt
      - Gtk+
      - FLTK
      - FOX
      - OpenGL
    - What platform-specific GUI toolkits exist for Python?
  - Tkinter questions
    - How do I freeze Tkinter applications?
    - Can I have Tk events handled while waiting for I/O?
    - I can’t get key bindings to work in Tkinter: why?

## 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; wxWidgets 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 for more details.

wxWidgets is an extension module that wraps many of the wxWindows C++ classes, and is quickly gaining popularity amongst Python developers. You can get wxWidgets as part of the source or CVS distribution of wxWindows, or directly from its home page.

#### Qt

There are bindings available for the Qt toolkit (PyQt) and for KDE (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 PyQt license from Riverbank Computing and (up to Qt 4.4; Qt 4.5 upwards is licensed under the LGPL license) a Qt license from Trolltech.

#### Gtk+

PyGtk bindings for the Gtk+ toolkit have been implemented by by James Henstridge; see ftp://ftp.gtk.org/pub/gtk/python/.

#### 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?

The Mac port 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, Python programs can use MacOS X’s Cocoa libraries. See the documentation that comes with the Mac port.

Pythonwin 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 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.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).

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