I\'m having a very weird problem with Python\'s pytz: it seems to have an incomplete catalog of timezones on my system (MacOS X 10.8.5, system Python 2.7.5).
I cannot say why your installation of pytz is broken, but here's a possible fix:
pip show pytz.open /System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python (replacing my path with yours if different). This will launch a Finder window with your Python modules.