Somehow pip stopped working on my NixOS :-(
$ nix-shell
New python executable in /home/matthias/source/tbconnect/firmware/.venv/bin/python2.7
Not overwriting existing python script /home/matthias/source/tbconnect/firmware/.venv/bin/python (you must use /home/matthias/source/tbconnect/firmware/.venv/bin/python2.7)
Installing pip, wheel...
done.
Traceback (most recent call last):
File "/home/matthias/source/tbconnect/firmware/.venv/bin/pip", line 6, in <module>
from pip._internal.main import main
ImportError: No module named main
