If you receive the following error below, you can try reinstalling PIP.

For example:

sudo apt-get remove --purge python-pip

curl https://bootstrap.pypa.io/get-pip.py | sudo python

Or

easyinstall pip

#############[ FATAL ERROR ]#############

Non zero exit status (1) for:

pip --version

With response:

Traceback (most recent call last):
File "/usr/local/bin/pip", line 7, in <module>
from pip._internal import main
ImportError: No module named _internal