When pip3 gives errors on "No module named 'pip._internal'"

fixpip3.md

How to fix No module named 'pip._internal'

$ pip3

Traceback (most recent call last):
File "/home/qinyu/.local/bin/pip3", line 7, in <module>
   from pip._internal import main
ModuleNotFoundError: No module named 'pip._internal'

This doesn't work:

$ sudo apt-get --reinstall install python3

This works: Get a file from here, then

$ sudo python3 get-pip.py