You may wonder why there are two different Python wrappers for Qt and how different they are?
PyQt and PySide are actually very similar, so similar that the code below for a Qt based version of the miles-to-kilometers converter works with both PyQt and PySide. For PySide you only have to replace the import line at the beginning. The short answer lies mainly in license related issues.
PyQt is significantly older than PySide and at one time had a larger community and was usually ahead when it comes to adopting new developments. It is mainly developed by Riverbank Computing Limited and distributed under GPL v3 and a commercial license. Releases follow a regular schedule and the software is generally considered very robust, mature, and well supported.
PySide is developed by Nokia and had its initial release in 2009, in a time when Nokia was the owner of Qt. As can be read on the PySide 1.2.4's pypi page, PySide has been developed and published in response to a lack of a Qt wrapper for Python that has a suitable license for FOSS and proprietary software development. Without going too much into the details of the different license models involved, if you want to develop a commercial application, PyQt requires you to pay fees for a commercial license, while the LGPL license of PySide permits application in commercial projects. PySide's popularity has recently surpassed PyQt, and is now more likely to be referenced and used and is frequently listed first in search results.
From an educational perspective, it doesn’t really matter whether you use PySide or PyQt. As we already indicated, the programming interfaces have over the recent years converged to be very similar, at least for the basic GUI based applications we are going to develop in this course. However, we have some specific reasons to continue with PyQt that will be listed at the end of the next section.