pip's configparser dependency breaks backports namespace conventions

[Chaz M]

This is specifically a problem with the debundling of the pip package, see https://github.com/pypa/pip/issues/6149 for further discussion.

Environment
pip version: python-pip (9.0.1-2.3)
Python version: Python 2.7.15+
OS: Ubuntu 18.10

Description
The python-pip package (at least on Ubuntu 18.10) depends on the python-configparser package, which dumps a blank __init__.py into the /usr/lib/python2.7/dist-packages/backports directory. However, backports should instead be defined as a namespace package (see PEP 420 and https://pypi.org/project/backports/). While this is not good in general, this is particularly problematic for pip because the some of packages it installs do not work as a result!

Expected behavior
pip should be able to install backports packages, which can then be imported without error.

How to Reproduce
After installing python-pip, run command pip install backports.shutil_which (the specific backports package does not particularly matter)
Then run from backports.shutil_which import which inside a python shell
An error occurs.

Output
>>> from backports.shutil_which import which
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named shutil_which```

[Dan Kegel (dank)]

This just cost me four hours on Ubuntu 18.04.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Dan Kegel (dank)]

More specifically, if I do

pip install backports.os
python -c "from backports import os"

it fails as described. But if I then do

sudo apt remove python-configparser

it succeeds.

[Chaz M (chazzz)]

I believe this has been fixed in the configparser source, thanks to Jason R. Coombs (https://github.com/jaraco/configparser/issues/17).

[Dan Kegel (dank)]

I suspect this was the cause of https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=865359