[Distutils] bizarre behavior with wheels and namespace packages

[Brian Wickman]

Not sure if this belongs on distutils-sig or import-sig, but I'm
experiencing slightly odd behavior with wheels and namespace packages.

Fetch a namespace package source distribution, e.g. twitter.common.python,
and build two copies of it, one with bdist_egg and one with bdist_wheel.

This leaves me with:
twitter.common.python-0.3.1-py2.6.egg
twitter.common.python-0.3.1-py26-none-any.whl

Explode them into the following directories (respectively):
egg_dist
whl_dist

Then attempt:

PYTHONPATH=egg_dist python -c 'import twitter.common.python'

(works)

PYTHONPATH=whl_dist python -c 'import twitter.common.python'

(drumroll)

Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: No module named twitter.common.python

This is slightly unexpected.  Absent from the .whl distribution are the
__init__.pys with the proper declare_namespace declarations.  Even more
bizarrely:

PYTHONPATH=whl_dist python -c 'import pkg_resources'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File
"/Users/wickman/Python/CPython-2.6.9/lib/python2.6/site-packages/pkg_resources.py",
line 2736, in <module>
    add_activation_listener(lambda dist: dist.activate())
  File
"/Users/wickman/Python/CPython-2.6.9/lib/python2.6/site-packages/pkg_resources.py",
line 698, in subscribe
    callback(dist)
  File
"/Users/wickman/Python/CPython-2.6.9/lib/python2.6/site-packages/pkg_resources.py",
line 2736, in <lambda>
    add_activation_listener(lambda dist: dist.activate())
  File
"/Users/wickman/Python/CPython-2.6.9/lib/python2.6/site-packages/pkg_resources.py",
line 2274, in activate
    list(map(declare_namespace,
self._get_metadata('namespace_packages.txt')))
  File
"/Users/wickman/Python/CPython-2.6.9/lib/python2.6/site-packages/pkg_resources.py",
line 1870, in declare_namespace
    path = sys.modules[parent].__path__
KeyError: 'twitter'

So even pkg_resources is surprised as well.  If I do the following:

PYTHONPATH=whl_dist python -c 'import site; site.addsitedir("whl_dist");
import twitter.common.python'

then it works, since the twitter.common.python-0.3.1-py2.6-nspkg.pth gets
processed properly and module.__path__s populated accordingly.  I would
expect pkg_resources to handle this fine but apparently it doesn't.

Any ideas?  Bug in pkg_resources, wheel or PEBKAC?

Thanks!
~brian
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