"UndefinedEnvironmentName" error with setuptools-20.6

[warner]

The tahoe-1.11.0 release was only a few hours old when we started getting reports of failures. It looks like setuptools made a release today that breaks many packages. (In fact, they made seven releases today, which can't be a good sign).

​https://github.com/pypa/setuptools/issues/523 is the setuptools bug. Apparently most 20.5.* and 20.6.* versions are broken. The recommended workaround (verified by warner and cypher) is to downgrade to setuptools-20.4, e.g.:

(venv) % pip install setuptools==20.4

The symptom is that pip install tahoe-lafs works normally, but then actually trying to run tahoe gives a traceback like the following:

  File "/ve/lib/python2.7/site-packages/pkg_resources/_vendor/packaging/markers.py", line 278, in evaluate
    return _evaluate_markers(self._markers, current_environment)
  File "/ve/lib/python2.7/site-packages/pkg_resources/_vendor/packaging/markers.py", line 203, in _evaluate_markers
    lhs_value = _get_env(environment, lhs.value)
  File "/ve/lib/python2.7/site-packages/pkg_resources/_vendor/packaging/markers.py", line 185, in _get_env
    "{0!r} does not exist in evaluation environment.".format(name)
pkg_resources._vendor.packaging.markers.UndefinedEnvironmentName: 'extra' does not exist in evaluation environment.

I'm hoping that they'll make a new release tomorrow that fixes the problem, but in the meantime, if you see this error, try downgrading your setuptools.

[warner]

Setuptools-20.6.7 has fixed the problem (they reverted the change that triggered it, and will try again in some later release). So a newly-upgraded virtualenv ought to be ok now.

They've removed almost all of the broken versions from pypi: it is still possible to install 20.6.6 (which breaks for me), but 20.5 and 20.6.0-20.6.5 are no longer on pypi (which also means I can't easily test them to identify exactly which ones were broken).

So: if you see this problem, do a pip install --upgrade setuptools. If the problem persists and pip list reports a setuptools of 20.6.7 or later, please re-open this ticket and give us the details.