err, no. if you write an external module using only python code, as long as you use a gpl-compatible python to run zope, you can call your external code from zope. if you write a product suclassing dc code, you're effectively 'linking' and gpl limitations apply.
GPL limitations apply to whom: To you, the developer? To a downstream user invoking the product via dtml-call or dtml-var or their pythonish equivalents? To a downstream developer who modifies your product and redistibutes the modified product? To a downstream developer who writes a component that invokes the GPL component?
In my mind the only sensible answers are developer - no, user - no (but see Jerome Alet's codacil), downstream modifier - yes, downstream developer who uses - no.
The only other sensible option is that, indeed, no one may distribute GPL components for Zope, including the original developer.
as i said before, writing gpl code subclassing zope is a non-sense. even the author cannot, imho, redistribute its work with a plain gpl attached to it. the gpl says that if you link with gpl code *all* the code should be gpl or gpl-compatible (major os components like clibs, compilers, etc are an exception). so even the author cannot do that without licensing under gpl plus some exception ("as a special exception you're allowed to link this code with zope or any other zope product distributed under the zpl".) see the (in)famous gpl vs. qt thread in the debian mailing lists for an in-depth analisys of this problem.
ciao, federico
OK, this is essentially what I wanted. Now the problem is completely distilled. DC and FSF somehow have to come to some understandings of the following questions. Can a GPL (unmodified) component be distributed for Zope (at all)? Can a GPL (modified per fog) component be distributed for Zope? If yes to either, may the component be invoked (dtml-var, dtml-call, or equivalent) from a non-GPL component? If yes to either, may the component be subclassed by a non-GPL component? Jim
-- Federico Di Gregorio MIXAD LIVE Chief of Research & Technology fog@mixadlive.com Debian GNU/Linux Developer & Italian Press Contact fog@debian.org The number of the beast: vi vi vi. -- Delexa Jones