qt_backport

qt_backport makes unmodified python code based on Qt4 work with Qt5.

More specifically (and currently), if you have PyQt5 installed and functional, but want to work with older PyQt4 or PySide code without having to do any conversion work, this package is for you!

Installation

1. Uninstall any existing Qt4 wrapper (PyQt4 or PySide) if you have one.
2. Install PyQt5
3. pip install qt_backport

Usage

qt_backport automatically makes both 'PyQt4' and 'PySide' packages available that will function like the old Qt4 versions, but will actually be backed by PyQt5.

ie: your old code like this will just work as-is:

import PyQt4
from PyQt4 import QtCore
from PyQt4.QtGui import *  #<-- this is supported, but yuck

or

import PySide
from PySide import QtCore
from PySide.QtGui import *  #<-- this is supported, but yuck

When to use qt_backport?

This package is particularly useful when you have installed a modern Qt5 wrapper (currently only PyQt5) and are trying to learn Qt using legacy code examples you find on the web.

qt_backport is not primarily intended as a method for porting your applications from Qt4 to Qt5 (you are better off converting if you can), but it does do a good job of this and can definitely help get you started.

Why is qt_backport needed at all?

When Qt4 was updated to Qt5 there was a major reorganization done to the class organization. In addition, there have been many other API changes.

One of the most significant changes was that a huge number of classes that used to be contained within 'QtGui' were dispersed out to various other locations instead. eg: All of the widgets were moved out of QtGui and into a new module called QtWidgets. Although the new locations make much more sense, it broke a lot of old code. qt_backport is a hack to make old code work as-is.

There have been many more API changes in the Qt 4.x to Qt 5.2 transition (Qt 5.2 is current the time of writing this). qt_backport deals with many of these changes, but all of them may not be captured (yet). A simple example of such a change (that qt_backport handles) is that QColor.dark() was removed and replaced with QColor.darker() in Qt 4.3.

Note that, although the backport generally works quite well, there may be additional changes you need to make to to your old code for it to work. These changes depend on the vintage of your old code. For example, old style signal/slot connections are not currently supported.

NOTE: At the current time, the only Qt wrapper for python that works with Qt5 is PyQt5. In future this may change (eg: when PySide upgrades to use Qt5).

How does it work?

qt_backport wraps Qt using PyQt5 (currently the only python wrapper for Qt5), but provides an emulation layer that emulates both the PySide and the PyQt4 APIs. Installing qt_backport automatically makes the PySide and PyQt4 emulators available for import.

This is easier to see visually:

                   +-----------------------------------+
                   |                                   |
                   | Existing Python code that expects |
                   |     the PyQt4 or PySide API       |
                   |                                   |
                   +-------+------------------+--------+
                           |                  |
                          OLD          <with qt_backport>
                          WAY                 |
                           |            +-----+-------+
                           |            |             |
qt_backport                |            |  PySide or  |
Emulation layer:           |            |    PyQt4    |
                           |            |             |
                           |            +-----+-------+
                           |                  |
                  +--------+--------+   +-----+-------+
                  |                 |   |             |
Wrapper layer:    | PySide or PyQt4 |   |   PyQt5     |
                  |                 |   |             |
                  +--------+--------+   +-----+-------+
                           |                  |
                      +----+-----+        +---+-----+
                      |          |        |         |
Qt library layer:     |   Qt4    |        |   Qt5   |
                      |          |        |         |
                      +----------+        +---------+

To do:

• support old-style connections (ie: connect(app, SIGNAL(), app, SLOT())

• support more known api changes

  • API change coverage is currently not 100%, being mostly driven by demand for certain classes/methods. Coverage is currently quite good, though.
  • other potential changes are covered here: http://qt-project.org/doc/qt-5/portingguide.html

• unit tests for the zillion api patches

License

MIT. See LICENSE file.