[Import-SIG] PEP 420: Implicit Namespace Packages

[Eric V. Smith]

I'm working on finishing up the PEP 420 work. I think the PEP itself is
complete. If you have any comments, please send them to me or this list.

The implementation at features/pep-420 has been merged with the recent
importlib changes to the 3.3 branch. I've implemented support in the
import machinery itself, as well as modified the filesystem finder
(FileFinder) and the zipimport finder.

About the only question I have is: Is everyone okay with the changes to
the finders, described in the PEP? Basically they now return a string in
addition to a loader or None. If they return a string, then the string
represents the path of a possible namespace package portion. The change
is backward compatible: unmodified finders will just be unable to
participate in a namespace package.

Barry Warsaw, Jason Coombs, and I are sprinting this Thursday. We'll
focus on adding tests, and maybe documentation if we have time. If
anyone has any concerns I'd like to hear them before then so that we can
work on addressing them.

The changes themselves are very small. I think the diff is a total of
maybe 40 lines of code. Yury Selivanov had mentioned backporting to 3.2
(which I assume would be an unsupported-by-python-dev effort). I
actually don't think it would be all that complicated.

Eric.