Circular imports in pip._vendor.requests

Looks like since pip 18.1 there’s a circular import problem. All versions including 18.1 and 19.1.1 produce something like this (traceback from 19.1.1 release):

Traceback (most recent call last):
  File "/usr/local/bin/pip", line 7, in <module>
    from pip._internal import main
  File "/usr/local/lib/python2.7/dist-packages/pip/_internal/__init__.py", line 40, in <module>
    from pip._internal.cli.autocompletion import autocomplete
  File "/usr/local/lib/python2.7/dist-packages/pip/_internal/cli/autocompletion.py", line 8, in <module>
    from pip._internal.cli.main_parser import create_main_parser
  File "/usr/local/lib/python2.7/dist-packages/pip/_internal/cli/main_parser.py", line 12, in <module>
    from pip._internal.commands import (
  File "/usr/local/lib/python2.7/dist-packages/pip/_internal/commands/__init__.py", line 6, in <module>
    from pip._internal.commands.completion import CompletionCommand
  File "/usr/local/lib/python2.7/dist-packages/pip/_internal/commands/completion.py", line 6, in <module>
    from pip._internal.cli.base_command import Command
  File "/usr/local/lib/python2.7/dist-packages/pip/_internal/cli/base_command.py", line 25, in <module>
    from pip._internal.index import PackageFinder
  File "/usr/local/lib/python2.7/dist-packages/pip/_internal/index.py", line 39, in <module>
    from pip._internal.utils.packaging import check_requires_python
  File "/usr/local/lib/python2.7/dist-packages/pip/_internal/utils/packaging.py", line 10, in <module>
    from pip._internal import exceptions
ImportError: cannot import name exceptions

Contents of the bin script:

$ cat `which pip`                                                                                                                                  #!/usr/bin/python2.7

# -*- coding: utf-8 -*-
import re
import sys

from pip._internal import main

if __name__ == '__main__':
    sys.argv[0] = re.sub(r'(-script\.pyw?|\.exe)?$', '', sys.argv[0])
    sys.exit(main())

Note that 18.0 doesn’t have the problem.

This happens on Ubuntu 18.04 if it matters (yes, pip is installed globally, python-pip deb package not installed of course).

[ionelmc]

There’s still some crappy code if importing something from vendor first makes everything fall apart imo. Sure, from an user’s perspective it doesn’t matter (no one should be doing that) but from an maintainer’s perspective you gonna get bitten by that sooner or later.

[chrahunt]

I think we can leave this open until such a test is implemented or someone has a good argument against it.

I had put this previously in #6498 (comment), and after trying to implement it my argument against this test would be that we would have to either:

1. exclude vendored dependencies, which wouldn’t’ve helped this situation, or
2. maintain a platform-specific blacklist of modules for our vendored dependencies, which would be a decent amount of effort for very little benefit