pip install --upgrade pip breaks pip (new version 19.2.3)

[gneiss15]

• Pip version: Installed 8..1.1, Updated version 19.2.3
• Python version: 2.7.12
• Operating system: Ubuntu 16.04 LTS

After doing a
pip install --upgrade pip
starting pip results in:
Traceback (most recent call last):
File "/usr/bin/pip", line 9, in
from pip import main
ImportError: cannot import name main

[userNeptune]

same problem here

[pradyunsg]

Yea. There's nothing actionable here for pip developers -- Debian modifies the pip that they ship to users via apt, which breaks things in weird ways like this.

Please look at #5599.

[pfmoore]

But also, to be clear, you should not be upgrading system-supplied packages wihout using the system package manager (in this case apt) as explained in #5599 which @pradyunsg referenced.

[gneiss15]

OK, that seams to be the problem.
Unfortunaly pip mentions/request to do the upgrade.
Is says something like:
a new version ... is available, please upgrade by using 'pip install...'
.. and after doing so, pip is broken :-(
OK, reinstaling it using apt solves the problem.
Who knows (before Your answer pfmoore) that ubuntu modifies pip ?