[PyQt] A nasty licencing question

David Boddie david at boddie.org.uk
Mon Jul 30 18:52:11 BST 2018

On Mon Jul 30 14:19:54 BST 2018, Sampsa Riikonen wrote:

> This is exactly what I was talking about.
> So, if at a certain moment, you don't have the PyQt license and add the
> following line into your code:
> from PyQt import ...
> Then that's it.  Your code will be forever GPL .. it became GPL at the
> very moment you distributed it (uploaded to the internet).  You can't
> use it anymore in any other context that GPL.  Even removing those
> damning lines wont save it.

As others have pointed out this is completely wrong. If you wrote the code,
you can still distribute it under another license. The recipient of the code
you distributed is receiving it under the terms of the GPL. If they go and
get your code from your website under its original license they can use it
under that license.

It would be hard for anyone to tell if they had got the original from your
website or received it in a GPL-licensed work if the code was identical,
but that's also the case if they received it in a LGPL-licensed work.

> If the author claims that the module has a MIT (or any other license),
> the people using that module must find out if the author had a valid
> PyQt license at the moment he distributed it.. otherwise they step on
> the license landmine (a nice legal limbo)

This conclusion follows from what you said before, which is wrong. It has
nothing to do with having a PyQt license (GPL or commercial).

> However, if you write
> # from PyQt import ..  # be aware of the licensing consequences
> from PySide2 import ..
> Then the licensing landmine doesn't go off, as the first line is a
> comment only, not actual code.  Funny world.  :)

Unless you fail to follow the terms of the LGPL correctly.

I wanted to add an example to my previous mail but thought it might confuse
people, but maybe it's worth mentioning: Qt is supplied with a load of third
party libraries, many with permissive licenses. It is certainly _not_ the
case that they are all now licensed under the GPL. Nobody except the author
can relicense the code for an individual library unless the license for that
library allows it.


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