'ModuleNotFoundError' No module named 'tomli' after installing using pip and venv

[mateuszkojro]

Describe the bug

After installing black using pip inside venv running it results in 'ModuleNotFoundError' No module named 'tomli' exception beeing raised:

To Reproduce

1. Create new virtual environment and activate it

python -m venv venv

and

.\venv\Scripts\activate.ps1

3. pip install black
4. black --version

output:

Traceback (most recent call last):
  File "C:\Users\PC1080Ti\AppData\Local\Programs\Python\Python38\lib\runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Users\PC1080Ti\AppData\Local\Programs\Python\Python38\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "C:\Users\PC1080Ti\Downloads\black-repro-bug\venv\Scripts\black.exe\__main__.py", line 4, in <module>
  File "src\black\__init__.py", line 45, in <module>
  File "c:\users\pc1080ti\downloads\black-repro-bug\venv\lib\site-packages\black\files.py", line 32, in <module>
    import tomli as tomllib
ModuleNotFoundError: No module named 'tomli'

Expected behavior
output:

black, 22.12.0 (compiled: yes)
Python (CPython) 3.8.8rc1

Environment

• Black's version: 22.12.0
• OS and Python version: Windows (21H2 19044.2364) running Python 3.8.8rc1

Additional context
The same behavior is observed when installing black from the main branch. 

[JelleZijlstra]

tomli is a dependency for 3.8: https://github.com/psf/black/blob/main/pyproject.toml#L70

I can't reproduce this on MacOS with 3.8.10. The one thing that stands out in your report is that you're using 3.8.8rc1: maybe something is mishandling deps for RC versions.

[mateuszkojro]

Hi,
This might indeed be the issue with Python versions using the postifx notation since Tomli is automatically installed for Python 3.10.9 and not for 3.10.0b1 (I cannot test it for 3.8 because they no longer provide those on the official website).

[JelleZijlstra]

@ichard26 looked into this with me on Discord and found:

• The root cause is a bug in packaging, fixed in allow pre-release versions in marker evaluation pypa/packaging#523
• pip hasn't yet updated packaging to pick up this fix
• We can prevent getting hit by this bug by changing our version requirement to python_version < '3.11' instead of listing a specific alpha. I'm about to submit a PR doing that.

[mateuszkojro]

Tested in my environment and it solves it. Thanks a lot!

[NavyaAJ]

I've reproduced this issue on mac today after the Python update to 3.11. Later realised I hadn't changed the version of Python in ci.yaml.
So the conclusion is that this issue can occur when the version of black installed for 3.10 is not compatible with 3.11

Error details:
`Traceback (most recent call last):

File "/opt/hostedtoolcache/Python/3.10.12/x64/bin/black", line 5, in

from black import patched_main

File "src/black/init.py", line 52, in

File "/opt/hostedtoolcache/Python/3.10.12/x64/lib/python3.10/site-packages/black/files.py", line 27, in

import tomli as tomllib

ModuleNotFoundError: No module named 'tomli'

Error: Process completed with exit code 1.`