[Zope-dev] setup.py "extra" dependencies

[Martijn Faassen]

Hi there,

I know opinions are divergent about 'extra' dependencies in setup.py. 
These ar dependencies that effectively make a single project with a 
single dependency structure into a number of "virtual" packages that 
each can have a separate list of dependencies. Such a virtual package 
that we're currently getting rid of is zope.component[zcml].

I think they make the graph harder to reason about. That's bad, we want 
to reason about the system more easily. So I propose that:

* we shouldn't create any new "extra" dependencies from now on.

* we should investigate ways to remove the need for 'extra' dependencies.

The latter point would of course not be done instantly, but if we agree 
we don't want to create *more* "extra" dependencies we can agree on 
starting with that policy right away.

One place where "extra" dependencies are used quite a lot is in testing.
One extra dependency that shows up a lot is a dependency on 
zope.app.testing. I think that *also* makes things much harder to reason 
about; testing dependencies should follow normal package dependencies.

I therefore think zope.app.testing is one package we should be looking 
to get rid of eventually by splitting it up among a lot of 'testing' 
modules in individual packages. This way we won't have zope.app.testing
sitting at an edge against our whole dependency tree. Since this is a 
lot of work this will be an ongoing project but we could at least agree 
we *want* to do this.

Opinions?

Regards,

Martijn