Why is PIP raising an AssertionError on pip freeze?

Reason: The python-pip package in Ubuntu 12.04 is seriously outdated and has some bugs with certain package names (as I can see) and cannot parse them correctly.

Solution: install a newer version of pip, via easy_install.

This worked for me (running Ubuntu, both 12 and 14 LTS):

pip install -U setuptools
pip install -U pip

Upgrade to the latest version of setuptools in order to be able to upgrade to the latest version of pip, and upgrade to the latest version of pip to get a version that has fixed the AssertException error.