My console:
desarrollador@desarrollador-HP-14-Notebook-PC1:~$ pip freeze Exception: Traceback (most recent call last): File \"/usr/lib/python2.7/dist
Reason: The python-pip package in Ubuntu 12.04 is seriously outdated and has some bugs with certain package names (as I can see) and cannot parse them correctly.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.