In short, don't do this. You shouldn't be emitting signals from outside the class. The factory example above isn't very useful, because you're not defining custom methods on those classes to emit those signals. Typically, this is how you would utilize custom signals. Jun 13, 2018 The addRandomTextSlot( self ) addition is the slot we attached to the Random Text push-button in the GUI, using Designer. The pyuic5 utility does not seem to generate code for it, and it's left up to us to do. Try running the newly created file with Python 3: python3 mainwindow.py You should see the GUI as illustrated above. Flip between the two tabs to verify that both have been populated. I am currently in the process of creating a class that produces a pyqtSignal(int) and pyqtSlot(int). The difficulty lies in creating a signal that emits a specific value. Suppose I want to produce. Aug 27, 2019 These PyQt examples show you how to create a desktop app with Python and Qt. Start with 'Hello World' or browse the official PyQt demos. You can run every example yourself on Windows, Mac or Linux. All you need is Python 3. For instructions, please see below. Running the examples is really easy.

If you start building Python application with Qt5 you'll soon discover that there are in fact two packages which you can use to do this — PyQt5 and PySide2.

In this short guide I'll run through why exactly this is, whether you need to care (spoiler: you really don't), what the few differences are and how to work around them. By the end you should be comfortable re-using code examples from both PyQt5 and PySide2 tutorials to build your apps, regardless of which package you're using yourself.

Background

Why are there two packages?

PyQt has been developed by Phil Thompson of Riverbank Computing Ltd. for a very long time — supporting versions of Qt going back to 2.x. Back in 2009 Nokia, who owned the Qt toolkit at the time, wanted to have Python bindings for Qt available under the LGPL license (like Qt itself). Unable to come to agreement with Riverbank (who would lose money from this, so fair enough) they then released their own bindings as PySide (also, fair enough).

Edit: it's called PySide because 'side' is Finnish for 'binder' — thanks to Renato Araujo Oliveira Filho in the comments.

The two interfaces were comparable at first but PySide ultimately development lagged behind PyQt. This was particularly noticeable following the release of Qt 5 — the Qt5 version of PyQt (PyQt5) was available from mid-2016, while the first stable release of PySide2 was 2 years later.

It is this delay which explains why many Qt 5 on Python examples use PyQt5 rather than PySide2 — it's not necessarily better, but it existed. However, the Qt project has recently adopted PySide as the official Qt for Python release which should ensure its viability and increase it's popularity going forward.

PyQt5	PySide2
Current stable version (2019-06-23)	5.12	5.12
First stable release	Apr 2016	Jul 2018
Developed by	Riverbank Computing Ltd.	Qt
License	GPL or commercial	LGPL
Platforms	Python 3	Python 3 and Python 2.7 (Linux and MacOS only)

Which should you use? Well, honestly, it doesn't really matter.

Both packages are wrapping the same library — Qt5 — and so have 99.9% identical APIs (see below for the few differences). Code that is written for one can often be used as-is with other, simply changing the imports from PyQt5 to PySide2. Anything you learn for one library will be easily applied to a project using the other.

Also, no matter with one you choose to use, it's worth familiarising yourself with the other so you can make the best use of all available online resources — using PyQt5 tutorials to build your PySide2 applications for example, and vice versa.

In this short chapter I'll run through the few notable differences between the two packages and explain how to write code which works seamlessly with both. After reading this you should be able to take any PyQt5 example online and convert it to work with PySide2.

Licensing

The key difference in the two versions — in fact the entire reason PySide2 exists — is licensing. PyQt5 is available under a GPL or commercial license, and PySide2 under a LGPL license.

If you are planning to release your software itself under the GPL, or you are developing software which will not be distributed, the GPL requirement of PyQt5 is unlikely to be an issue. However, if you plan to distribute your software commercially you will either need to purchase a commercial license from Riverbank for PyQt5 or use PySide2.

Qt itself is available under a Qt Commercial License, GPL 2.0, GPL 3.0 and LGPL 3.0 licenses.

Python versions

PyQt5 is Python 3 only
PySide2 is available for Python3 and Python 2.7, but Python 2.7 builds are only available for 64 bit versions of MacOS and Linux. Windows 32 bit is supported on Python 2 only.

UI files

Both packages use slightly different approaches for loading .ui files exported from Qt Creator/Designer. PyQt5 provides the uic submodule which can be used to load UI files directly, to produce an object. This feels pretty Pythonic (if you ignore the camelCase).

The equivalent with PySide2 is one line longer, since you need to create a QUILoader object first. Unfortunately the api of these two interfaces is different too (.load vs .loadUI) and take different parameters.

To load a UI onto an object in PyQt5, for example in your QMainWindow.__init__, you can call uic.loadUI passing in self (the target widget) as the second parameter.

The PySide2 loader does not support this — the second parameter to .load is the parent widget of the widget you're creating. This prevents you adding custom code to the __init__ block of the widget, but you can work around this with a separate function.

Converting UI files to Python

Both libraries provide identical scripts to generate Python importable modules from Qt Designer .ui files. For PyQt5 the script is named pyuic5 —

You can then import the UI_MainWindow object, subclass using multiple inheritance from the base class you're using (e.g. QMainWIndow) and then call self.setupUI(self) to set the UI up.

For PySide2 it is named pyside2-uic —

The subsequent setup is identical.

For more information on using Qt Designer with either PyQt5 or PySide2 see the Qt Creator tutorial.

exec() or exec_()

Pyqt5 Signals And Slots Tutorial

The .exec() method is used in Qt to start the event loop of your QApplication or dialog boxes. In Python 2.7 exec was a keyword, meaning it could not be used for variable, function or method names. The solution used in both PyQt4 and PySide was to rename uses of .exec to .exec_() to avoid this conflict.

Pyqt5 Signals And Slots

Python 3 removed the exec keyword, freeing the name up to be used. As PyQt5 targets only Python 3 it could remove the workaround, and .exec() calls are named just as in Qt itself. However, the .exec_() names are maintained for backwards compatibility.

PySide2 is available on both Python 3 and Python 2.7 and so still uses .exec_(). It is however only available for 64bit Linux and Mac.

If you're targeting both PySide2 and PyQt5 use .exec_()

Slots and Signals

Defining custom slots and signals uses slightly different syntax between the two libraries. PySide2 provides this interface under the names Signal and Slot while PyQt5 provides these as pyqtSignal and pyqtSlot respectively. The behaviour of them both is identical for defining and slots and signals.

The following PyQt5 and PySide2 examples are identical —

Or for a slot —

If you want to ensure consistency across PyQt5 and PySide2 you can use the

Pyqt5 Signals And Slots Example