Running the PEP 561 tests causes FileNotFoundErrors on Windows

[Michael0x2a]

I'm currently getting a few FileNotFoundError test failures when I try running the mypy tests from master -- I'm guessing this PR is most likely the culprit?

The test outputs are a little long, so I included them in this gist: https://gist.github.com/Michael0x2a/5d022c29a305dab2f028bab84271b213

I'm currently running mypy on Windows 10. Also, I'm not sure if any of this matters or not, but I can also confirm I get the same results whether or not I use powershell or cmd, whether or not I'm running in administrator mode... I'm happy to run more experiments to help narrow down the issue if needed.

@ethanhs -- any ideas?

[emmatyping]

Did you pull master since #5225 ?

[Michael0x2a]

Yeah -- I pulled about 10-15 min ago.

[emmatyping]

Ah, I missed that the first time looking at the output. I will take a closer look soon.

[ilevkivskyi]

FWIW these tests are failing on my Mac with very similar error.

[emmatyping]

Hm, that is unfortunate. Would either of you be able to drop into pdb before this line https://github.com/python/mypy/blob/master/mypy/test/testpep561.py#L65 and tell me if the path in python_executable actually exists on disk?

[Michael0x2a]

It seems apparently not. The temp folder itself exists, but appears to be empty. (So, C:\Users\Michael\AppData\Local\Temp\tmpw5ox88q1 exists, but not C:\Users\Michael\AppData\Local\Temp\tmpw5ox88q1\Scripts or C:\Users\Michael\AppData\Local\Temp\tmpw5ox88q1\Scripts\python, for example.)

[Michael0x2a]

Out of curiosity, I tried modifying the virtualenv function directly so it prints the output of run_command if the return code isn't zero -- it seems the issue was that I didn't have the virtualenv package installed. I tried pip-installing it, and everything is working again!

So I guess this is really my fault -- that package is apparently listed in test-requirements.txt and I admittedly haven't looked at that file in a long while...

It might be nice if we added a custom error message though -- or maybe add the missing error code check in the virtualenv function.

[gvanrossum]

Also (OT) virtualenv is no longer needed, use venv instead, it's in the stdlib.

[emmatyping]

Also (OT) virtualenv is no longer needed, use venv instead, it's in the
stdlib.

AIUI, venv cannot create a virtualenv for another python executable, which is needed for the Python 2 tests :/

I will make a PR to print errors for the virtualenv creation.

[ilevkivskyi]

Yes, installing virtualenv solves the issue for me as well.

[emmatyping]

Sorry all for the trouble!

[gvanrossum]

venv cannot create a virtualenv for another python executable, which is needed for the Python 2 tests

Oh, wow, I did not know it could do that. Makes sense then.