Comment 1 for bug 383171

The source timezone lists are hardcoded in pytz/__init__.py, and are identical on all installations. However, they are filtered at runtime to cope with missing timezone data files (a number of installations are modified to use the system installed timezone data rather than the files distributed with pytz). I think the difference you see could be caused by an incompatible version or a bug in the pkg_resources module, which is normally distributed as part of setuptools.

pkg_resources doesn't seem to contain a version identifier, so I'm not sure how to check what version is installed.

Upgrading pkg_resources to the latest version might solve the problem.

pkg_resources is needed if the timezone data files are inside a .egg. We can avoid using pkg_resources unless absolutely necessary by checking for the existence of the calculated data file path on disk first, and only attempting to load using pkg_resources.resource_stream if that file does not exist.