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Re: Python library under permissive GPL-compatible license optionally using GPL library

Yaroslav Halchenko wrote:
Dear fellas who know much more about licensing than me.

I might have even asked before (since we are in a similar situation with
PyMVPA/shogun) but forgot what was the summary:

If we have a library X in Python, released under some GPL-compatible
license (e.g. BSD-3 or Expat) and then using (optionally) some GPL code
(at run time) provided by another library Y -- what are the implications?
Am I wrong on any of the following statements

- the project X codebase doesn't have to be relicensed to GPL
- the project X can use project Y (since under GPL compatible license)

- It is only at 'run time' when actual linking to the library Y happens,
   so project must comply with GPL but whose responsibility it is then
   and what needs to be enforced?

   - original distributor of X must have provided all the sources with
     modifications?  But it was user's decision to use GPL'ed library

   - or user must somehow make sure he has the sources... (sounds

- is mere ability to be used with GPL licensed library Y makes
   distributors of code of X required to comply with GPL? (e.g. provide
   modified sources)

Thanks in advance for your feedback

[1] http://mail.scipy.org/pipermail/nipy-devel/2014-December/010707.html
If the distributor were a distro like Debian IMHO:
- package X can be licensed under Expat
- package Y is licensed under GPL (I would probably add a warning on the description)

As package X already meets GPL requeriments that's not really a problem.

However, let's call X' to X + GPL-incompatible changes.

Then X' and Y couldn't be used together.

I suppose that if X' distributor actively encourage its users to use Y with its incompatible X',
he could be deemed liable for encouraging those copyright violations.
(this is quite different from simply allowing generic modules to be loaded)

You may be interested in the linking-with-libreadline story.

For your case I would simply document it (on a license page, when listing
modules for download… it will depend on your website structure)

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