On Guix fa122ac4ca2bd4c87b216e2f478397bcde2c1d8f.

This works:

--8<---------------cut here---------------start------------->8---
/gnu/store/czfix13276dvibyf0l4lbk92wiinha37-python-pip-20.0.2/bin/pip install -r requirements/dev.txt
--8<---------------cut here---------------end--------------->8---

But this does not:

--8<---------------cut here---------------start------------->8---
$ guix install python-pip
$ pip install -r requirements/dev.txt

Traceback (most recent call last):
  File "/path/to/myprofile/bin/pip", line 6, in <module>
    from pip._internal import main
  File "/path/to/myprofile/lib/python3.8/site-packages/pip/_internal/__init__.py", line 40, in <module>
    from pip._internal.cli.autocompletion import autocomplete
  File "/path/to/myprofile/lib/python3.8/site-packages/pip/_internal/cli/autocompletion.py", line 8, in <module>
    from pip._internal.cli.main_parser import create_main_parser
  File "/path/to/myprofile/lib/python3.8/site-packages/pip/_internal/cli/main_parser.py", line 11, in <module>
    from pip._internal.commands import (
  File "/path/to/myprofile/lib/python3.8/site-packages/pip/_internal/commands/__init__.py", line 6, in <module>
    from pip._internal.commands.completion import CompletionCommand
  File "/path/to/myprofile/lib/python3.8/site-packages/pip/_internal/commands/completion.py", line 6, in <module>
    from pip._internal.cli.base_command import Command
  File "/path/to/myprofile/lib/python3.8/site-packages/pip/_internal/cli/base_command.py", line 26, in <module>
    from pip._internal.index import PackageFinder
ImportError: cannot import name 'PackageFinder' from 'pip._internal.index' (/path/to/myprofile/lib/python3.8/site-packages/pip/_internal/index/__init__.py)
--8<---------------cut here---------------end--------------->8---

-- 
Pierre Neidhardt
https://ambrevar.xyz/