PyQT Licensing and plugins/scripting

[Phil Thompson]

On Friday 03 December 2004 2:50 pm, Fabio wrote:
> Hi all,
> I'm about to write an application, and I'd like to use PyQt, but before
> choosing this toolkit I would like to clarify some particular licensing
> issues; if some user has already touched these, I would like to hear from
> his experiences.
>
> This app should be cross-platform, so, given qt licensing policies, I would
> buy a commercial PyQt license and a commercial Qt license.
>
> Could I license the application under the GPL for Gnu/Linux and under a
> commercial license for Windows and Mac OS X?

As there is are GPL versions of Qt and PyQt for Mac OS X, it's only Windows 
you need to handle differently.

> If this is possible, I guess 
> that contributions to the GPLed version could not be incorporated in the
> commercial version, but this would not be a big problem.

"Minor" contributions you don't need to worry about. I think that the GPL FAQ 
covers what is considered "minor". For significant contributions you would 
need to get the agreement of the contributors beforehand. Some projects state 
that contributions will only be accepted if the copyright of those 
contributions are transferred to the main project author.

> The main issue with licensing is that I would like to give users of the
> application a scripting framework (for macros and the like), and eventually
> a plugin framework; PyQT redistribution policy states that if an user can
> get in touch with PyQT directly it should have a commercial license itself;
> how does this apply to those who want to develop commercial PyQT
> applications with a plugin/scripting framework?

The key is access to the Qt API. If your applications gives the users access 
to the API then those users are developers and need their own licenses. On 
the other hand if the API is sufficiently removed from the Qt API then you 
shouldn't have a problem. Your API should restrict itself to extending the 
capabilities of your application - the more general purpose you make it, the 
more you risk a visit from the lawyers.

Phil