[SciPy-user] Re[2]: ANN: Veusz 0.5 - a scientific plotting package

[Prabhu Ramachandran]

>>>>> "Robert" == Robert Kern <rkern at ucsd.edu> writes:

    >> Maybe it would be possible to dual-licence the code if anyone
    >> would like to use it??

    Robert> Depending on how you and Trolltech and Riverbank Computing
    Robert> interpret the situation, the Qt-specific parts can
    Robert> probably only be considered GPLed.  For users of the GPLed
    Robert> versions of PyQt, this shouldn't pose a problem as their
    Robert> code would have deal with the GPL license of PyQt
    Robert> regardless.  Users of the non-GPL versions would be in a
[...]

I don't completely understand this.  Lets say I subclass a PyQt class
called QWidget and call it SomeQtWidget, I also use a bunch of other
PyQt widgets but don't extend them.  Lets say I define this class in
sqw.py.  Can I legally distribute sqw.py separately under the BSD (or
some GPL compatible license)?  My impression is that any extension to
a GPL'd library *must* be GPL and therefore sqw.py must be released
under the GPL?  Right or wrong?  

Now, given the segment of the GPL that you quoted, if I did have a
'model' class (in the MVC world-view) separate from the SomeQWidget
then I could release the model code under any license I choose.
Right?

However, if you look at sqw.py it isn't clear that sqw.py is really
modifying PyQt.  The "linking" really happens at runtime.  There are
no header files, nothing in PyQt is really "modified" or copied, no
binary program that links to PyQt.  So why should sqw.py be
distributed as GPL code in the first place?  How then does the GPL
differ from the LGPL in this context?

cheers,
prabhu