bpo-36751: Deprecate getfullargspec and report positional-only args as regular args

[pablogsal]

https://bugs.python.org/issue36751

[zooba]

Looks good to me. Thanks, Pablo! 👍

[tirkarthi]

This generates DeprecationWarning in two tests in Lib/unittest/test/testmock/testhelpers.py. Please wrap it with self.assertWarns(DeprecationWarning) or better use inspect.signature in the two assert calls to remove the DeprecationWarning.

➜  cpython git:(pr_13016) ./python.exe Lib/unittest/test/testmock/testhelpers.py
...................................................../Users/karthikeyansingaravelan/stuff/python/cpython/Lib/inspect.py:1114: DeprecationWarning: Use inspect.signature() instead of inspect.getfullargspec()
  warnings.warn("Use inspect.signature() instead of inspect.getfullargspec()",
.............
----------------------------------------------------------------------
Ran 66 tests in 0.832s

OK

[pablogsal]

Done in 74639b3. Thanks @tirkarthi, good catch!

[tirkarthi]

LGTM. Thanks @pablogsal .

[ncoghlan]

Please revert this change - this API was deliberately undeprecated, as per https://bugs.python.org/issue27172 and PEP 570 isn't sufficient justification to deprecate it again.

[ncoghlan]

Slight correction: the API fixes to restore compatibility with 3.7 are a good thing, the problem is the reintroduction of the programmatic deprecation warnings, even though the reasons for leaving them out still hold.

[pablogsal]

@ncoghlan I have opened #13245 to handle the undeprecation. Sorry for the inconvenience.