Qt.py 2.0.2

Qt.py enables you to write software that runs on any of the 4 supported bindings - PySide6, PyQt6, PySide2, PyQt5.

News

• More details.

Guides

• Qt 6 Transition Guide
• Developing with Qt.py
• Dealing with Maya 2017 and PySide2
• Vendoring Qt.py
• Udemy Course
• PythonBytes #77 (Starts at 5:00)

Table of contents

• Project goals
• Install
• Usage
• Documentation
  • Environment Variables
  • Subset
  • Branch binding-specific code
  • Override preferred choice
  • QtSiteConfig.py
  • Compile Qt Designer files
  • Loading Qt Designer files
• Rules
• How it works
• Known problems
• Who's using Qt.py?
• Projects using Qt.py
• Projects similar to Qt.py
• Developer guide

Project goals

Write once, run in any binding.

Qt.py was born in the film and visual effects industry to address the growing need for software capable of running with more than one flavor of the Qt bindings for Python - PySide6, PySide2, PyQt6 and PyQt5.

See CONTRIBUTING.md for more details.

Install

Qt.py is a single file and can either be copy/pasted into your project, downloaded as-is, cloned as-is or installed via pip or conda.

# From PyPI
$ pip install Qt.py

# From Anaconda
$ conda config --add channels conda-forge
$ conda install qt.py

• Pro tip: Never use the latest commit for production. Instead, use the latest release. That way, when you read bug reports or make one for yourself you will be able to match a version with the problem without which you will not know which fixes apply to you nor would we be able to help you. Installing via pip or conda as above ensures you are provided the latest stable release. Unstable releases are suffixed with a .b, e.g. 1.1.0.b3.
• Pro tip: Supports vendoring

Usage

Use Qt.py as you would use PySide6.

import sys
from Qt import QtWidgets, QtCompat

app = QtWidgets.QApplication(sys.argv)
button = QtWidgets.QPushButton("Hello World")
button.show()
QtCompat.QApplication.exec_()

• Also see /examples

Documentation

All members of Qt stem directly from those available via PySide6, along with these additional members.

Example

>>> from Qt import __binding__
>>> __binding__
'PyQt5'

Compatibility

Qt.py also provides compatibility wrappers for critical functionality that differs across bindings, these can be found in the added QtCompat submodule.

Example

>>> from Qt import QtCompat
>>> QtCompat.loadUi

Class specific compatibility objects

Note: Most of these are for Qt4 and Qt5 compatibility. With 2.0 dropping support for Qt4 many of them are no longer needed, but we are leaving them in for backwards compatibility.

Between Qt4 and Qt5 there have been many classes and class members that are obsolete. Under Qt.QtCompat there are many classes with names matching the classes they provide compatibility functions. These will match the PySide2 naming convention.

from Qt import QtCore, QtWidgets, QtCompat
header = QtWidgets.QHeaderView(QtCore.Qt.Horizontal)
QtCompat.QHeaderView.setSectionsMovable(header, False)
movable = QtCompat.QHeaderView.sectionsMovable(header)

This also covers inconsistencies between bindings. For example PyQt4's QFileDialog matches Qt4's return value of the selected. While all other bindings return the selected filename and the file filter the user used to select the file. Qt.QtCompat.QFileDialog ensures that getOpenFileName(s) and getSaveFileName always return the tuple.

Environment Variables

These are the publicly facing environment variables that in one way or another affect the way Qt.py is run.

Subset (or "common members")

Members of Qt.py is a subset of PySide6. Which means for a member to be made accessible via Qt.py, it will need to (1) be accessible via PySide6 and (2) each of the other supported bindings. This excludes large portions of the Qt framework, including the newly added QtBluetooth and QtQuick3D modules but guarantees that anything you develop with Qt.py will work identically on any binding - PySide2, PySide6, PyQt5 and PyQt6. If you need to use such excluded modules with Qt.py, please see QtSiteConfig.py.

We call this subset "common members" and these can be generated by running the tox tests. The membership tests will output all modules and members of each binding into individual JSON files. These JSON files are then compared and a /.members/common_members.json file is generated. The contents of the members dictionary of this file is copy-pasted into the _common_members dictionary of Qt.py. Please note that the script will only use the most up-to-date set of VFX Platform-stipulated software versions.

See the wiki for a breakdown of what members are common across the supported Qt python bindings:

• Qt.py<1.4: PySide2, PyQt5, PySide, PyQt4
• Qt.py==1.4.*: PySide6, PyQt6, PySide2, PyQt5, PySide, PyQt4
• Qt.py==2.0.*: PySide6, PyQt6, PySide2, PyQt5. (Minimum Qt version 5.13)

Branch binding-specific code

Some bindings offer features not available in others, you can use __binding__ to capture those.

if "PySide" in __binding__:
  do_pyside_stuff()

Override preferred choice

If your system has multiple choices where one or more is preferred, you can override the preference and order in which they are tried with this environment variable.

$ set QT_PREFERRED_BINDING=PyQt5  # Windows
$ export QT_PREFERRED_BINDING=PyQt5  # Unix/OSX
$ python -c "import Qt;print(Qt.__binding__)"
PyQt5

Constrain available choices and order of discovery by supplying multiple values.

# Try PyQt5 first and then PySide2, but nothing else.
$ export QT_PREFERRED_BINDING=PyQt5:PySide2

Using the OS path separator (os.pathsep) which is : on Unix systems and ; on Windows.

If you need to control the preferred choice of a specific vendored Qt.py you can use the QT_PREFERRED_BINDING_JSON environment variable instead.

{
    "Qt":["PyQt5"],
    "myproject.vendor.Qt":["PyQt5"],
    "default":["PySide2"]
}

This json data forces any code that uses import Qt or import myproject.vendor.Qt to use PyQt5(from x import Qt etc works too, this is based on __name__ of the Qt.py being imported). Any other imports of a Qt module will use the "default" PySide2 only. If "default" is not provided or a Qt.py being used does not support QT_PREFERRED_BINDING_JSON, QT_PREFERRED_BINDING will be respected.

# Try PyQt6 first and then PyQt5 for the Qt module name space.
$ export QT_PREFERRED_BINDING_JSON="{"Qt":["PyQt6","PyQt5"]}"
# Use PySide2 for any other Qt module name spaces.
$ export QT_PREFERRED_BINDING=PySide2

QtSiteConfig.py

Add or remove members from Qt.py at run-time.

• Examples

If you need to expose a module that isn't included in Qt.py by default or wish to remove something from being exposed in Qt.py you can do so by creating a QtSiteConfig.py module and making it available to Python.

1. Create a new file QtSiteConfig.py
2. Implement update_members
3. Expose to Python

# QtSiteConfig.py
def update_members(members):
    """Called by Qt.py at run-time to modify the modules it makes available.

    Arguments:
        members (dict): The members considered by Qt.py
    """
    members.pop("QtCore")

Finally, expose the module to Python.

$ set PYTHONPATH=/path/to
$ python -c "import Qt.QtCore"
ImportError: No module named Qt.QtCore

Linux and MacOS users, replace set with export

Compile Qt Designer files

WARNING - ALPHA FUNCTIONALITY
See #132 for details.

.ui files compiled via pyside2-uic inherently contain traces of PySide2 - e.g. the line from PySide2 import QtGui.

In order to use these with Qt.py, or any other binding, one must first erase such traces and replace them with cross-compatible code.

$ pyside2-uic my_ui.ui -o my_ui.py
$ python -m Qt --convert my_ui.py
# Creating "my_ui_backup.py"..
# Successfully converted "my_ui.py"

Now you may use the file as you normally would, with Qt.py

Loading Qt Designer files

The uic.loadUi function of PyQt5 and PyQt6 as well as the QtUiTools.QUiLoader().load function of PySide6/PySide2 are mapped to a convenience function loadUi.

import sys
from Qt import QtCompat, QtWidgets

app = QtWidgets.QApplication(sys.argv)
ui = QtCompat.loadUi(uifile="my.ui")
ui.show()
QtCompat.QApplication.exec_()

For PyQt bindings it uses their native implementation, whereas for PySide bindings it uses our custom implementation borrowed from the qtpy project.

loadUi has two arguments as opposed to the multiple that PyQt ships with. See here for details - in a nutshell, those arguments differ between PyQt and PySide in incompatible ways. The second argument is baseinstance which allows a ui to be dynamically loaded onto an existing QWidget instance.

QtCompat.loadUi(uifile="my.ui", baseinstance=QtWidgets.QWidget)

uifile is the string path to the ui file to load.

If baseinstance is None, the a new instance of the top-level widget will be created. Otherwise, the user interface is created within the given baseinstance. In this case baseinstance must be an instance of the top-level widget class in the UI file to load, or a subclass thereof. In other words, if you've created a QMainWindow interface in the designer, baseinstance must be a QMainWindow or a subclass thereof, too. You cannot load a QMainWindow UI file with a plain QWidget as baseinstance.

loadUi returns baseinstance, if baseinstance is provided. Otherwise it will return the newly created instance of the user interface.

Rules

The PyQt and PySide bindings are similar, but not identical. Where there is ambiguity, there must to be a clear direction on which path to take.

Governing API

The official Qt 6 documentation is always right. Where the documentation lacks answers, PySide6 is right.

For example.

# PyQt6 adheres to PySide6 signals and slots
PyQt6.Signal = PyQt6.pyqtSignal
PyQt6.Slot = PyQt6.pyqtSlot

Caveats

There are cases where Qt.py is not handling incompatibility issues. Please see CAVEATS.md for more information.

Known Problems

Send us a pull-request with known problems here!

• Maya and incompatible bindings on PYTHONPATH

Who's using Qt.py?

Send us a pull-request with your studio here.

• Atomic Fiction
• Bläck
• Blur Studio
• CGRU
• Colorbleed
• Digital Domain
• Disney Animation
• Dreamworks Animation
• Epic Games
• Fido
• Framestore
• ftrack
• Futureworks
• Industrial Brothers
• Industriromantik
• Mackevision
• Method Studios
• Mikros Image
• Moonbot Studios
• MPC
• Overmind Studios
• Psyop
• Raynault VFX
• Rising Sun Pictures
• Rodeo FX
• Sony Pictures Imageworks
• Spin VFX
• Weta Digital
• GermanTechJobs

Presented at Siggraph 2016, BOF!

Projects using Qt.py

Send us a pull-request with your project here.

• USD Manager
• Cosmos
• maya-capture-gui
• pyblish-lite
• pyvfx-boilerplate
• riffle
• cmt
• PythonForMayaSamples
• Kraken
• AFANASY
• Syncplay
• BlenderUpdater
• QtPyConvert
• Pyper

Projects similar to Qt.py

Comparison matrix.

Also worth mentioning, pyqt4topyqt5; a good starting point for transitioning to Qt.py.

Send us a pull-request with your project here.

Developer Guide

Tests are performed on each aspect of the shim.

• Functional
• Caveats
• Examples

Each of these are run under..

• Python 3.7
• Python 3.9
• Python 3.10
• Python 3.11

..once for each binding or under a specific binding only.

Each test is run within it's own isolated process, so as to allow an import to occur independently from other tests. Process isolation is handled via nosepipe.

Tests that are written at module level are run four times - once per binding - whereas tests written under a specific if-statement are run only for this particular binding.

if binding("PyQt5"):
    def test_something_related_to_pyqt5():
        pass

Code convention

Below are some of the conventions that used throughout the Qt.py module and tests.

• Etiquette: PEP8
  • All code is checked using ruff check and format. Use tox -e check,format.
• Etiquette: Double quotes
  • " = yes, ' = no.
• Etiquette: Napoleon docstrings
  • Any docstrings are made in Google Napoleon format. See Napoleon for details.
• Etiquette: Semantic Versioning
  • This project follows semantic versioning.
• Etiquette: Underscore means private
  • Anything prefixed with an underscore means that it is internal to Qt.py and not for public consumption.

Running tests

Due to the nature of multiple bindings and multiple interpreter support, setting up a development environment in which to properly test your contraptions can be challenging. So here is a guide for how to do just that using tox.

Setup:

You will need to install python 3.7 or higher. It's recommended that you install python 3.7, 3.9, 3.10 and 3.11 so you can test all supported versions of python but tox is configured to allow you to skip test for missing python versions. However when the tests run on github all versions of python are required to work.

Install tox using pip in your preferred version of python. pip install tox For the rest of this guide it's assumed that you have this version of python added to your PATH env var and can run the command tox.

Running tox

When running tox, its expected that you are in a terminal and have cd'd into the root of the git checkout.

To run all tests run the command tox. This will run all default tests in order sequentially. This lets you see all output from each test as it runs. This project is configured run tests in parallel using tox -p. This lets you run all of the tests much quicker but you only see output if there is a problem.

A successful run should generate output similar to this once finished:

  membership-begin: OK (0.16=setup[0.06]+cmd[0.09] seconds)
  membership-py39-PySide5.15: OK (0.38=setup[0.02]+cmd[0.36] seconds)
  membership-py39-PyQt5.15: OK (0.28=setup[0.02]+cmd[0.27] seconds)
  membership-py311-PySide6.5: OK (0.67=setup[0.08]+cmd[0.59] seconds)
  membership-py311-PyQt6.7: OK (0.42=setup[0.14]+cmd[0.28] seconds)
  membership-end: OK (0.17=setup[0.00]+cmd[0.17] seconds)
  test-begin: OK (0.06=setup[0.00]+cmd[0.06] seconds)
  test-py37-PySide5.13-impl: OK (11.03=setup[5.59]+cmd[1.22,4.22] seconds)
  test-py37-PySide5.13-caveats: OK (7.05=setup[5.64]+cmd[1.17,0.24] seconds)
  test-py37-PySide5.13-examples: OK (7.78=setup[5.61]+cmd[1.20,0.61,0.36] seconds)
...
  test-py311-PyQt6.5-impl: OK (9.45=setup[6.81]+cmd[2.64] seconds)
  test-py311-PyQt6.5-caveats: OK (7.09=setup[6.80]+cmd[0.30] seconds)
  test-py311-PyQt6.5-examples: OK (7.86=setup[6.81]+cmd[0.72,0.33] seconds)
  congratulations :) (13.30 seconds)

Running all tests is useful for verifying that there are no problems, but when you run into a problem its useful to only run one or a couple of tests. You can use the -e flag to specify specific test names. When using -e you have to pass specific test names you want to run as a comma separated list. Any of the test names(text before the : OK) listed above can be used.

Running a single test:

tox -e membership-py311-PySide6.5

Running multiple tests:

tox -e membership-begin,membership-py311-PySide6.5,membership-py311-PyQt6.7,membership-end

This would run just those 4 tests.

The membership-begin is used to clean up files left from previous tests. The next to jobs are used to run specifically configured tests in this case generating a list of bindings for PySide6 and PyQt6 in python 3.11. The membership-end job is used to combine the files generated by the previous tests.

The Github Actions are using the same tox configuration to run all of the tests which means that when the tests pass on your machine, they pass on Github Actions. And everybody wins!

See CONTRIBUTING.md for more of the good stuff.

Test breakdown

• Tests starting with membership- are used to generate the common members dictionary. These are written into the /.members directory.
  • membership-begin removes files created by the other membership tests to ensure the new test run doesn't have old data.
  • membership-*-* Each test uses a specific version of python and Qt to generate a mapping of members available.
  • membership-end combines the data generated by each membership-*-* into the final common members dictionary for all Qt versions as well as per-major Qt version. It also creates some reference .md files to make it easy to see all possible members and which bindings implement them.
• Tests starting with test- are used to run the testing suite on a specific set of python and Qt.
  • test-begin generates files needed to run the other tests.
  • test-*-*-impl runs implementation tests defined in test.py.
  • test-*-*-caveats tests the code found in CAVEATS.md.
  • test-*-*-examples tests the code found in /examples.

Upload to PyPI

To make a new release onto PyPI, you'll need to have the correct permissions and:

1. Increment version in Qt.py
2. Make a new release here on GitHub, see prior releases for naming-scheme; but in short, it's the version string. No prefix or suffix.
3. The rest is automated, the release ends up on PyPI shortly thereafter

Qt 6 Transition Guide

Removed Members (Qt.py==2.*)

With the removal of support PySide and PyQt4 Qt.QT_SIP_API_HINT was removed. Qt.IsPySide and Qt.IsPyQt4 remain for compatibility, but will always return False now.

Removed Members (Qt.py==1.4.*)

Many members were removed from Qt.py due to no longer existing in PySide 6 and PyQt6. They were removed to support Qt 4, 5 and 6.

"QtCore": [
    "QAbstractState",
    "QAbstractTransition",
    "QEventTransition",
    "QFinalState",
    "QSignalTransition",
    "QT_TR_NOOP_UTF8",
    "QTextCodec",
    "QTextDecoder",
    "QTextEncoder",
    "QtCriticalMsg",
    "QtDebugMsg",
    "QtFatalMsg",
    "QtSystemMsg",
    "QtWarningMsg",
    "qChecksum",
    "qIsNull",
    "QPictureIO"
],
"QtGui": [
    "qIsGray"
]
"QtMultimedia": [
    "QAbstractVideoBuffer",
    "QAbstractVideoSurface",
    "QAudio",
    "QAudioDeviceInfo",
    "QAudioFormat",
    "QAudioInput",
    "QAudioOutput",
    "QVideoFrame",
    "QVideoSurfaceFormat"
],
"QtNetwork": [
    "QNetworkConfiguration",
    "QNetworkConfigurationManager",
    "QNetworkSession"
],
"QtOpenGL": [
    "QGL",
    "QGLContext",
    "QGLFormat",
    "QGLWidget"
],
"QtSql": [
    "QSql",
    "QSqlDatabase",
    "QSqlDriver",
    "QSqlDriverCreatorBase",
    "QSqlError",
    "QSqlField",
    "QSqlIndex",
    "QSqlQuery",
    "QSqlQueryModel",
    "QSqlRecord",
    "QSqlRelation",
    "QSqlRelationalDelegate",
    "QSqlRelationalTableModel",
    "QSqlResult",
    "QSqlTableModel"
],
"QtWidgets": [
    "QActionGroup",
    "QDesktopWidget",
    "QDirModel",
    "QKeyEventTransition",
    "QMouseEventTransition",
    "QUndoCommand",
    "QUndoGroup",
    "QUndoStack"
],
"QtX11Extras": [
    "QX11Info"
],
"QtXml": [
    "QXmlAttributes",
    "QXmlContentHandler",
    "QXmlDTDHandler",
    "QXmlDeclHandler",
    "QXmlDefaultHandler",
    "QXmlEntityResolver",
    "QXmlErrorHandler",
    "QXmlInputSource",
    "QXmlLexicalHandler",
    "QXmlLocator",
    "QXmlNamespaceSupport",
    "QXmlParseException",
    "QXmlReader",
    "QXmlSimpleReader"
],
"QtXmlPatterns": [
    "QAbstractMessageHandler",
    "QAbstractUriResolver",
    "QAbstractXmlNodeModel",
    "QAbstractXmlReceiver",
    "QSourceLocation",
    "QXmlFormatter",
    "QXmlItem",
    "QXmlName",
    "QXmlNamePool",
    "QXmlNodeModelIndex",
    "QXmlQuery",
    "QXmlResultItems",
    "QXmlSchema",
    "QXmlSchemaValidator",
    "QXmlSerializer"
]

Static Members Missing from Instances

An overall change is that instances of classes, like QFont() no longer provides access to static members, such as QFont.Bold. So things like:

font = QFont()
font.setWeight(font.Bold)

Must be replaced with:

font = QFont()
font.setWeight(QFont.Weight.Bold)

Or:

This method is not recommended.

font.setWeight(type(font).Weight.Bold)

Tedious and seemingly unnecessary.. But there you have it!

Note: You should also see Fully Qualified Enums

Notes

Qt.py 1.4.0, released in May 2024, added support for Qt 6 whilst preserving compatibility with Qt 4 and 5. That means that in most cases, code you've already written for Qt 4 or 5 will now continue to work with Qt 6, such as Maya 2025.

However, some changes between 5 and 6 require up-front work by you the developer to make your codebase run on Qt 6 whilst continuing to run on Qt 4 and 5.

The above is what we know, please do submit issues and pull-request with what else you find!

• https://github.com/mottosso/Qt.py/issues/new

See also

The official PySide2 to PySide6 transition guide, which is especially helpful since Qt.py is modeled after PySide2.

• https://doc.qt.io/qtforpython-6/gettingstarted/porting_from2.html