When comparing Tkinter vs PySide, the Slant community recommends Tkinter for most people. In the question“What are the best Python GUI frameworks/toolkits?” Tkinter is ranked 3rd while PySide is ranked 7th.
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Pros
Pro Free for commercial use
Pro Included in the standard Python library
You probably already have it, since it's included in the standard Python distributions.
Pro Easy to learn and get productive with
TkInter is a small library with a gentle learning curve compared to what’s out there. It has a straightforward API and is often the go-to choice for building quick GUIs for Python scripts.
Pro Building executables is less complicated
Compared to other GUI libraries, building executables for TkInter applications are simpler because TkInter is included in Python and has no other dependencies. This results in less complicated packaging requirements and smaller binary size.
Pro Fast
Pro Supported by the Qt Company
Qt for Python aka PySide2 is the official set of Python bindings supported by the Qt Company.
Pro Qt widgets
Possibility to use a traditional widget-based user interface.
Pro QtQuick/QML
Possibility to use a declarative approach to define the user interface.
Pro Weak copyleft
PySide is licensed under the LGPL, which makes it easier to incorporate into commercial projects than PyQt.
Cons
Con No advanced widgets
TkInter does not come with advanced widgets out of the box (e.g. date picker).
Con Not good looking
You need a lot of code to make it look good.
Con No reliable UI builder available
There is no tool in the same league as Qt Designer (PyQt) for TkInter.
Con Similar to PyQt, you need a C++ background. at least you can read C++ code
Qt's document is poor, and Qt for Python(PySdie) is even worse. this document assumes that you are already familiar with Qt. if you want to customize a Widget, you need to look at the Qt C++ source code to know what to do.