Quick start into GUI applications with PyQt5 and PySide2

Qt is a powerful framework for developing cross platform GUI applications. KDE Linux desktop environment uses it as well as many Open Source and commercial applications.

In this article I'll showcase how to use Qt in Python to make GUI applications (the very basics of it).

PyQt and PySide

For Python developers since long time PyQt binding were available. As of now there is also Qt for Python project that provides PySide2 bindings.

There is a very good comparison on machinekoder.com. In short PyQt bindings existed for much longer and are distributed on GPL or Commercial license. PySide2 is distributed on LGPL or Qt commercial license - which may make a difference in some legal cases. In terms of making simple apps there shouldn't be much differences aside of imports. For more complex ones there may be some.

You may find a lot of tutorials for PyQt due to it age. PyQt4 is the former main version while now we use PyQt5. Some code did change (like signals and slots syntax) but overall the workflow should be the same. If you pick up some older PyQt4 books keep that in mind (and the book may use Python 2 instead of 3).

There are also books and resources for PyQt5, like Create Simple GUI Applications with Python and PyQt5 while also having some online resources on learnpyqt.com.

PyQt and PySide can be installed as any other Python packages via PyPi. You should also install Qt development tools. Qt Designer is the desired application for now. It allows creating user interface of the app in a visual manner. On Linux it can be in a separate package while for macOS or Windows it will likely be with the official Qt development package (macOS package managers like homebrew may also have split packages).

A note on desktop applications

Compared to web development, common in the Python community, the GUI application development is less popular and it can get quite complex much quicker. Before developing an app check if a web variant isn't a better solution (no need to build, distribute, install etc.).

When creating an app with a GUI be sure to make the GUI follow look and feel of other similar apps - a.k.a. you should try not to reinvent styles or some widget placements unless you are making an app with non-standard UI. For each operating system or desktop platform there are Human interface guidelines that describe how applications should look and behave to meet user experience standards.

Qt does follow those guidelines and also tries to make widgets follow current style of the system - if you run your app on Windows or on macOS it will look like other apps of that particular OS as well as some widgets may look different or be placed in different spots of the window.

Kivy uses it own style and will not follow OS style and usability guidelines – everything is in your hands. Tkinter will follow the style to some extent although the widgets won’t look "as good" as in native apps.

Python standard library versus Qt

In Qt class reference you will find functionalities that are also covered by Python standard library or popular third party packages. For example you can find QFile, QDir classes that represent files and directories and with other related classes implement a lot of filesystem operations. You can even run a SQL query via QSqlQuery and more.

With such overlap one can wonder which solution should be used - Python or PyQt/PySide bindings to C++ classes of Qt? Overall I would advise using Qt path as much as possible. A lot of classes and widgets is inter-compatible - meaning one class can accept an instance of another, like accepting a QFile object or use QSqlQuery to populate a grid and more.

If the Qt usage seems overly complicated and you know you aren't loosing any of that "glue" then sure, you can also use a Python way of doing things.

Also note that a lot of Qt classes takes operating system differences into account which may not be handled as well by non-Qt Python package. Like if you want to print a file Qt has you covered while when trying pure Python solutions you would likely need more time and testing to see if it's cross-platform (like you even have QPrintDialog in Qt...).

QtDesigner is used to create the user interface of your app. It can cooperate with other Qt tools to create translation files for i18n-enabled apps or manage assets like images and other files used by the app.

Now it's time for some code...

For a full code commentary on making a simple app in PyQt and PySide you can check my tutorial at:

https://rk.edu.pl/en/quick-start-gui-applications-pyqt5-and-pyside2/