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Improve signature of __getitem__ for list and dict #96364

@sobolevn

Description

@sobolevn

Bug report

Right now both list and dict have incorrrect text signatures of __getitem__.
What is affected?

>>> help(list.__getitem__) Help on method_descriptor: __getitem__(...) x.__getitem__(y) <==> x[y] >>> help(dict.__getitem__) Help on method_descriptor: __getitem__(...) x.__getitem__(y) <==> x[y]

In constrast with __setitem__ and __delitem__:

>>> help(list.__setitem__) Help on wrapper_descriptor: __setitem__(self, key, value, /) Set self[key] to value. >>> help(dict.__setitem__) Help on wrapper_descriptor: __setitem__(self, key, value, /) Set self[key] to value. >>> help(dict.__delitem__) Help on wrapper_descriptor: __delitem__(self, key, /) Delete self[key].

It also affects .__text_signature__:

>>> list.__getitem__.__text_signature__ >>> dict.__getitem__.__text_signature__ >>> list.__setitem__.__text_signature__ '($self, key, value, /)' >>> dict.__setitem__.__text_signature__ '($self, key, value, /)'

And inspect.signature:

>>> inspect.signature(dict.__getitem__) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/Users/sobolev/.pyenv/versions/3.8.9/lib/python3.8/inspect.py", line 3105, in signature return Signature.from_callable(obj, follow_wrapped=follow_wrapped) File "/Users/sobolev/.pyenv/versions/3.8.9/lib/python3.8/inspect.py", line 2854, in from_callable return _signature_from_callable(obj, sigcls=cls, File "/Users/sobolev/.pyenv/versions/3.8.9/lib/python3.8/inspect.py", line 2308, in _signature_from_callable return _signature_from_builtin(sigcls, obj, File "/Users/sobolev/.pyenv/versions/3.8.9/lib/python3.8/inspect.py", line 2119, in _signature_from_builtin raise ValueError("no signature found for builtin {!r}".format(func)) ValueError: no signature found for builtin <method '__getitem__' of 'dict' objects> >>> inspect.signature(dict.__setitem__) <Signature (self, key, value, /)>

I think that this can be fixed quite easily!
My plan is to modify these two descriptions:

  1. {"__getitem__", (PyCFunction)list_subscript, METH_O|METH_COEXIST, "x.__getitem__(y) <==> x[y]"},
  2. PyDoc_STRVAR(getitem__doc__, "x.__getitem__(y) <==> x[y]");

With something like typeobject.c has: "__getitem__($self, key, /)\n--\n\nReturn self[key]."

Using clinic here seems impossible / overly-complex.

Should I send a PR for this? 🙂

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