Cannot import main from pip 18.0

Environment: Global Environment

• pip version: 18.0
• Python version: 3
• OS: Ubuntu 17.10 (Linux)

Description When upgraded from 9.0.3 to 18.0, it starts showing the following error constantly on each use of pip-

Traceback (most recent call last): File "/usr/bin/pip", line 9, in <module> from pip import main ImportError: cannot import name main

Expected behavior This should not be happen.

How to Reproduce Upgrade pip from version 9 to latest as pip install --upgrade pip and you are unable to use any features of pip anymore.

1. Get package from this link https://files.pythonhosted.org/packages/5f/25/e52d3f31441505a5f3af41213346e5b6c221c9e086a166f3703d2ddaf940/pip-18.0-py2.py3-none-any.whl.
2. Then try run e.g. pip install scikit-learn
3. ImportError occurs.

Output Following traceback:

Traceback (most recent call last): File "/usr/bin/pip", line 9, in <module> from pip import main ImportError: cannot import name main

[abhiTronix]

The Ubuntu’s python-pip-9.0.1 installed(via apt get python-pip) is conflicting with Latest pip-18.0 provided by pypa. So sudo rm -rf ~/.local/lib/python2.7/site-packages/(Beware!) removes the ubuntu’s python-pip and resolves the problem. Only one pip can exist on the system

[pradyunsg]

Please see #5599.