Today my previously working builds started exploding when using pip, like this:
$ pip --version
Traceback (most recent call last):
File "/home/travis/virtualenv/python3.6.7/bin/pip", line 7, in <module>
from pip._internal import main
File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pip/_internal/__init__.py", line 40, in <module>
from pip._internal.cli.autocompletion import autocomplete
File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pip/_internal/cli/autocompletion.py", line 8, in <module>
from pip._internal.cli.main_parser import create_main_parser
File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pip/_internal/cli/main_parser.py", line 12, in <module>
from pip._internal.commands import (
File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pip/_internal/commands/__init__.py", line 6, in <module>
from pip._internal.commands.completion import CompletionCommand
File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pip/_internal/commands/completion.py", line 6, in <module>
from pip._internal.cli.base_command import Command
File "/home/travis/virtualenv/python3.6.7/lib/python3.6/site-packages/pip/_internal/cli/base_command.py", line 25, in <module>
from pip._internal.index import PackageFinder
ImportError: cannot import name 'PackageFinder'
Here’s an example instance: https://travis-ci.com/github/cherrypy/cheroot/jobs/364037184#L232.
Also, there’s a lot of jobs with the same problem in that build: https://travis-ci.com/github/cherrypy/cheroot/builds/176792255.
It does not explode on Python 3.8, 3.7, 3.5, and 3.4.
It is broken on Python 3.6 and Python 2.7 (at least).