Use importlib to avoid module name clashes for pytest

[neumond]

This allows simple modification for pytest --import-mode=importlib to completely avoid module naming issue if you have fresh python (>=3.5). This skips modifying sys.path, guessing package names, attempting to correctly import __init__.py and directories. This is more than enough for usual pytest workflow, e.g. if you have unimportable tests directory with files like test_something.py.

[kxepal]

This is very useful! Any chances to get this merged?

[denis-trofimov]

Moscow Python Beer Meetup report rules!

[valignatev]

This would be very helpful

[sobolevn]

This is an amazing feature!

[neumond]

I've made additional checks to prove these changes actually work with pytest.
As expected, it requires only adding "importlib" to --import-mode choices.

[blueyed]

@RonnyPfannschmidt
What is your opinion on this?

[RonnyPfannschmidt]

this is a nice solution we can use as a temporary opt in, but im under the impression we are missing a deeper detail

however i don't have time in the near future to work deeply enough into the related topic to make a good case for those details

as such i believe a good way forward is to get this in, have it as opt-in in pytest an sort out the more detailed issues after the port to pathlib is complete

[nicoddemus]

We just need a CHANGELOG entry so we can merge this in. 👍

[nicoddemus]

Please update the CHANGELOG

[nicoddemus]

Let's wait a day or two to get #207 and #215 in the next release as well. 👍

[kxepal]

🎉
Thank you all!

[nicoddemus]

Thanks again @neumond for the great PR!

[blueyed]

@neumond
Do you plan adding creating a PR to add this to pytest (choices/help, doc)?
(just stumbled across via py's docstring)

[blueyed]

btw: would it still possible to support relative imports? (ImportError: attempted relative import with no known parent package)

[blueyed]

Created pytest-dev/pytest#5352.