So I'm making an application which uses the python module PySide2 which is under LGPL. What I'm planning is to sell my program and make it non-distributable by making a unique password-identification mechanism. Such as a client-server system where a unique IP address receives only one password. Does my program still hold LGPL in this case?

Link to PySide2 :

  1. PyPi : https://pypi.org/project/PySide2/

  2. Homepage : https://wiki.qt.io/PySide2

  • Are you aware that using an LGPL python module doesn't require you to release your program under LGPL also?
    – MadHatter
    May 18 '21 at 7:40
  • Wait really? So I just have to comply to the LGPL license for using their module? But the license FAQ on pyqt says : "It depends entirely on what license you are going to use to distribute your application. If your license is incompatible with the GPL then you need a commercial PyQt license. If your license is also incompatible with the LGPL then you also need a commercial Qt license. (Note that some parts of Qt, QtCharts and Qt Data Visualization for example, are licensed under the GPL rather than the LGPL.)"
    – Pranav P A
    May 18 '21 at 7:42
  • 1
    LGPLv3 requires that you ship your code in such a way that updated versions of the LGPLv3 library can be run by it, but with python my guess is that won't be a problem. Your bigger issue is that some of Qt, which the library invokes (if I understand correctly) is GPLv3 (as you note above). Are you using any of the GPLv3 parts of Qt via this library?
    – MadHatter
    May 18 '21 at 8:10
  • Actually I'm using PySide2 right now which is a LGPL version of PyQt
    – Pranav P A
    May 18 '21 at 8:19
  • 3
    Yes, though I note it's helpful if you actually link to all these things in your question, rather than assuming everyone else knows where to find them. But having found the PySide2 page, it says that "PySide2 is available under both Open Source (LGPLv3/GPLv2) and commercial license ... For more information, refer to the Qt Licensing page.", which in turn notes that some of Qt is GPL, not LGPL. Since I don't know which bits of Qt are made available by PySide2, I have to ask whether you're using any of the GPL bits.
    – MadHatter
    May 18 '21 at 8:22

If you use a third-party LGPL library/module in your system, there are just a few requirements you have to fulfill:

  • You need to inform your users that you use that library/module and that it is under the LGPL license
  • You must give your users the right and means to replace the LGPL library/module with a different version (that uses the exact same interface).

Nothing in these requirements prevents you from using a product-key or phone-home licensing scheme for your application.

Actually, even the GPL license does not forbid you to use a product key or similar. The rub there is that you must give your users the right to remove the check for a valid product key and distribute that version.

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