pip error after upgrade: ImportError: cannot import name ‘main’

Sometimes pip can be really sucks, after upgrade the pip version, then you call it afterwards, it will fail somehow.

$ pip install --user --upgrade pip
Collecting pip
  Using cached https://files.pythonhosted.org/packages/0f/74/ecd13431bcc456ed390b44c8a6e917c1820365cbebcb6a8974d1cd045ab4/pip-10.0.1-py2.py3-none-any.whl
Installing collected packages: pip
Successfully installed pip-8.1.1
You are using pip version 8.1.1, however version 10.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
ImportError: cannot import name 'main'
$ pip
Traceback (most recent call last):
  File "/usr/bin/pip3", line 9, in 
    from pip import main
ImportError: cannot import name 'main'

The problem is easily can be resolved by doing this:

$ hash -d pip