Python 3.8: DeprecationWarning: Use inspect.signature() instead of inspect.getfullargspec()

[hroncok]

A lot of Fedora packages, when rebuilt with Python 3.8.0a4 fail to collect tests with pytest:

+ /usr/bin/python3 -m pytest -v --pyargs numpy -k 'not big_arrays and not large_archive and not test_highest_available_pickle_protocol and not test_binomial and not test_hypergeometric and not test_scalar_exception_propagation'
============================= test session starts ==============================
platform linux -- Python 3.8.0a4, pytest-4.4.1, py-1.8.0, pluggy-0.9.0 -- /usr/bin/python3
cachedir: .pytest_cache
rootdir: /builddir/build/BUILD/numpy-1.16.3, inifile: pytest.ini
collecting ... collected 0 items / 1 errors

==================================== ERRORS ====================================
________________________ ERROR collecting test session _________________________
/usr/lib/python3.8/site-packages/_pytest/config/__init__.py:435: in _importconftest
    return self._conftestpath2mod[conftestpath]
E   KeyError: local('/builddir/build/BUILDROOT/numpy-1.16.3-2.fc31.x86_64/usr/lib64/python3.8/site-packages/numpy/conftest.py')

During handling of the above exception, another exception occurred:
/usr/lib/python3.8/site-packages/pluggy/manager.py:95: in register
    hookimpl = HookImpl(plugin, plugin_name, method, hookimpl_opts)
/usr/lib/python3.8/site-packages/pluggy/hooks.py:344: in __init__
    self.argnames, self.kwargnames = varnames(self.function)
/usr/lib/python3.8/site-packages/pluggy/hooks.py:167: in varnames
    spec = _getargspec(func)
/usr/lib/python3.8/site-packages/pluggy/hooks.py:130: in _getargspec
    return inspect.getfullargspec(func)
/usr/lib64/python3.8/inspect.py:1114: in getfullargspec
    warnings.warn("Use inspect.signature() instead of inspect.getfullargspec()",
E   DeprecationWarning: Use inspect.signature() instead of inspect.getfullargspec()
!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!
=========================== 1 error in 0.26 seconds ============================

Now I don't know if treating this DeprecationWarning as error is the default pytest behavior or specific projects (mis)configuration, but the warning comes from pluggy. We still have 0.9.0, but I see getfullargspec() even in master.

[nicoddemus]

Hi @hroncok,

Thanks for the report!

I think we should update pluggy to not use the deprecated function in Python 3.8.

[hroncok]

I agree. Any idea if it is pluggy, pytest or the tested project that handles the DeprecationWarning as an error?

[nicoddemus]

It should be the project itself which configures this.

[hroncok]

Thanks for clarifying.

[tirkarthi]

This was done as part of PEP 570 implementation in commit python/cpython@d5d2b454693 in alpha 4. There is a discussion in CPython about reverting the deprecation marked as release blocker for Python 3.8 beta 1 : https://bugs.python.org/issue36751#msg342156

[hroncok]

The discussion seems ongoing. I'd say that migrating to inspect.signature() is still a good way to go.

[hroncok]

This is the stuff that pluggy currently uses:

signature = inspect.signature(func)
args = tuple(signature.parameters)
defaults = tuple(param.default for param in signature.parameters.values() if param.default is not inspect.Parameter.empty)

[hroncok]

@nicoddemus You've assigned this to yourself. I'll try to test the above code and submit a PR if it works. Let me know if you are already in the middle of the same.