pip安装破碎(pkg_resources。find_distribution返回req.py-prepare_files中的空列表)

At some point my pip installation broke (I suspect when upgrading to Ubuntu 14.04) and I haven't been able to unbreak it by completely removing it and reinstalling (via synaptic package manager). It doesn't occur for all packages but for a few common ones such as autopep8 and even setuptools itself.At some point my pip installation broke (I susp