Pytest warning on readline

[stefaneidelloth]

If I use pytest-6.2.4, pytest-cov 2.12.1 and python 3.9.4 on Windows 10

with following commands:

pytest --cov src --cov-fail-under=98 --cov-report=term-missing

or simply

pytest

I get a warning:

....\app\winpython\python-3.9.4.amd64\lib\site-packages\pyreadline\py3k_compat.py:8
c:\python_env\app\winpython\python-3.9.4.amd64\lib\site-packages\pyreadline\py3k_compat.py:8: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3
, and in 3.10 it will stop working
return isinstance(x, collections.Callable)

-- Docs: https://docs.pytest.org/en/stable/warnings.html

=> Could please replace pyreadline or somehow hide the warning?

Related:
#8733
pyreadline/pyreadline#68

[The-Compiler]

Like you point out, the warning is coming from pyreadline. pytest doesn't use pyreadline, all it does is import readline for #1281.

[nicoddemus]

@The-Compiler is right, but I think we should drop that workaround given pyreadline is no longer maintained, and the workaround was introduced in 2015 by #1281.

I will open a PR. 👍

[The-Compiler]

Not sure about this. As evident by this issue people still seem to have pyreadline installed, and depending on how obscure the behavior with pyreadline and --pdb is, I'd rather have them see a deprecation warning (making them realize they should probably uninstall pyreadline) than having behavior which is probably much harder to track down.

[nicoddemus]

OK, let's discuss this over the PR then: #8848 👍

[RonnyPfannschmidt]

We can ask packaging if pyreadline is installed and/or guard the import with a warning recorder + trigger a pytest specific pytest warning

[The-Compiler]

The workaround is there specifically for pyreadline from what I understood.

[bluetech]

I briefly tried to understand what the original workaround was about. IIUC, when pyreadline is imported, it attaches to stdin/out/err, and bugs out if they're redirected. But I'm pretty sure that the debugging plugin suspends the capturing before calling Pdb(...) which imports readline. So I wonder why the workaround is even needed? I don't have a Windows machine, and pyreadline has some "keysyms" error on Linux, so can't try it myself.

[nicoddemus]

Good idea @bluetech, I've tried this myself:

1. Fresh Python 3.9 virtualenv, using latest main (e84ba80).
2. Install pyreadline.
3. Execute with pytest --pdb test_fail.py.

pdb is launched on failure, works OK. I see the warning:

test_fail.py::test
  E:\projects\pytest\.env39\lib\site-packages\pyreadline\py3k_compat.py:8: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3, and in 3.10 it will stop working
    return isinstance(x, collections.Callable)

If I comment out the workaround in pytest (_readline_workaround), same results, including the warning.

Even though pytest no longer imports readline, pyreadline installs a readline.py in site packages, which is imported automatically by the Python runtime, which still triggers the warning.

So in conclusion it seems it is safe to remove the workaround, because pytest works fine if pyreadline is installed.