pyqt4 & qt license

[Michael Torrie]

On 03/09/2013 09:45 PM, Vito De Tullio wrote:
> D. Xenakis wrote:
> 
>> Can someone develop a closed source but NON-commercial software, by using
>> PyQT4 GPL license?
> 
> no, by definition of GPL: if you are using a GPL library, you must 
> distribute your software as GPL.
> 
> (the GPL does not care about commercial / non commercial)
> 
> http://www.gnu.org/licenses/gpl-faq.html#IfLibraryIsGPL

Just to be clear here, the GPL isn't a magical license.  It doesn't
arbitrarily infect your code and force you to use the GPL on your own
code.  And no matter what license you use, you can re-license your code
later under any terms you wish, since you own the copyright on the code.

Here's the vital part: The moment you distribute your code, if you use a
GPL library, then unless you also release your code under the GPL also,
you are now in a copyright violation situation.  You have three options:

1. License your code in a compatible way so that you're following the
terms of the open source license the library you are using asks of you.
 IE release your source code under the terms of the GPL.

2. Remove the GPL'd library and either implement the lost functionality
yourself (also know as "write your own dang code"), or replace the GPL'd
library with an equivalent library under a different, compatible
license.  In the case of PyQt, this could be PySide, or maybe you decide
to use a completely different GUI toolkit.

3. Negotiate a proprietary license with the copyright holder (IE buy the
proprietary, royalty-free license from PyQt's authors.

If you are in a position where you have violated copyright, failure to
remedy it in a timely manner can cause you to be financially liable to
the copyright holders of the code you are mis-using.

Now, if you develop a program using PyQt and distribute it under the
terms of the GPL, that does not mean you have to keep your code under
the GPL.  You can close your source at any time and use, say, PySide
instead.  But any code you already distributed under the GPL remains in
the wild (supposing someone has a copy) under the GPL terms, even if
newer versions of your software adopt a new license.