[PyQt] licensing

Joel B. Mohler joel at kiwistrawberry.us
Thu Jun 23 21:32:47 BST 2011

On Thursday, June 23, 2011 04:33:20 am Phil Thompson wrote:
> On Wed, 22 Jun 2011 10:35:40 +0200, "KONTRA, Gergely"
> <pihentagy at gmail.com>
> wrote:
> > Hi all!
> > 
> > Maybe a bit offtopic and theoretical question:
> > 
> > Suppose I'd like to write an app in python and Qt. I evaluate the
> > possibilities, and see, that pyqt is more stable now, so I decide to
> > begin coding with it (with the free version). When I make this
> > decision, I already think to wait for a more complete/stable PySide
> > binding and distribute my code which uses PySide (with a less
> > restrictive license). Or I first release it with PyQt, but later on I
> > find PySide, which has a less restrictive license.
> > Is any of the above cases the violation of the License Terms? So is it
> > legal? Is it fair?
> > 
> > And consider another case: I begin to write my app with Pyside, and
> > later release a version with pyqt at some point. Can I later release a
> > newer PySide based version with license compatible with PySide (which
> > is not compatible with pyqt's license)?
> > 
> > Yet another case: I do a prototype with PyQt, and than hand-convert it
> > to Qt/C++.
> You haven't said what license you want to use for your code. If you use
> the GPL version of PyQt then your license must be compatible with the GPL.

Sure, that's true *while* the application uses PyQt, but what about *after* 
PyQt is replaced with PySide?  I suppose one could argue that there is some 
ethical commitment due to the history, but I'm not seeing any commitment in a 
legal technical sense.  I think that after all technical reliance from PyQt is 
replaced by technical reliance on PySide, the project is free to relicense is 
it wishes in compliance with the reliance on PySide.

Or think about it this way:  I write a large project using a GPL library.  I 
wish to have more control so I clean-room re-implement the GPL library.  I'm 
now the sole author of the entire relevant software stack and I believe I'm 
free of the GPL.  I don't see how the fact that Nokia (in the case of 
PySide/PyQt) is the one bank-rolling the clean-room reimplementation changes 


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