zope.configuration failure to find dependency

While trying to upgrade zope.configuration for Nixos, I found this problem, which sounds similar to:

https://github.com/pypa/setuptools/issues/870

I tried already with Setuptools 32.3.1, but the result is the same. This is not Nix specific, but happens also in a normal Python3.6 virtualenv

======================================================================
ERROR: test_wo_parents (zope.configuration.tests.test_docutils.Test_makeDocStructures)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/tmp/zope.configuration/src/zope/configuration/tests/test_docutils.py", line 61, in test_wo_parents
    from zope.interface import Interface
ModuleNotFoundError: No module named 'zope.interface'

----------------------------------------------------------------------
Ran 252 tests in 0.195s

FAILED (errors=229)
Test failed: <unittest.runner.TextTestResult run=252 errors=229 failures=0>
error: Test failed: <unittest.runner.TextTestResult run=252 errors=229 failures=0>

[mwhudson]

So I encountered this too and my impression as to why this is failing is that it’s because the namespace package’s __path__ ends up being a importlib._bootstrap_external._NamespacePath object with Python 3.5 and 3.6 and there is an isinstance(path, list) in pkg_resources at https://github.com/pypa/setuptools/blob/master/pkg_resources/__init__.py#L2128 that prevents the __path__ being modified in some way that seems to be important (my guess is that it means the if _normalize_cached(item)==normalized: condition in file_ns_handler never fires, but I’m waaaaay past the point where I understand what’s going on now).

[FRidh]

In Nixpkgs we recently changed the way we install setuptools from egg to wheel. All packages, including setuptools are explicitly on PYTHONPATH during installation. Importing namespace packages such as zope however fails in case of Python 2.