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

Hi Yaroslav,

Le Fri, Dec 12, 2014 at 12:07:41PM -0500, Yaroslav Halchenko a écrit :
> 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)

Right.  Much of the GPL is about redistribution, not use.

> - 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

If the distributor of X distributes only X and asks the users to do all the
extra work, then it does not have to redistribute the sources of Y.

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


> - 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)

No, but the distributors of X would start to have obligations if they would
distribute X and Y together, for instance as a binary form.

In the case of Debian, since our archive contains the source packages, package-X
can depend on package-Y or contain code derived from package-Y without needing
extra work on the redistribution.  (Of course, the maintainer of package-X has to
ensure that liceses are compatible).

> [1] http://mail.scipy.org/pipermail/nipy-devel/2014-December/010707.html

If a third party download X and Y from their original distributors, and
redistribute the combination as binary code without the source, then they will
violate the GPL.  Thus, even if X is their main interst, if they download Y
because X needs it, they need to read Y's license.  If X provides some download
scripts for Y, it would be kind to write somewhere in the documentation that Y
is GPL-licensed.

Have a nice week-end,

Charles Plessy
Tsurumi, Kanagawa, Japan

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