Calling inspect.signature with an AsyncMock instance raises an exception

Bug report

Starting in Python 3.10.6, the following code raises an exception:

from inspect import signature
from unittest.mock import AsyncMock

mock = AsyncMock()
signature(mock)

No exception is raised when Mock is used.
The exception does not occur with Python 3.10.5.

Your environment

CPython versions tested on: 3.10.4, 3.10.5, 3.10.6 (Only occurs in 3.10.6)
Operating system and architecture: Windows 10, Linux (Official Docker Image)

Linked PRs

Related? #94924

This could be due to commit 4261b6b

(myenv) ➜  cpython git:(main) ./python
Python 3.12.0a0 (heads/main:575f8880bf, Aug 23 2022, 19:59:51) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import inspect
>>> from unittest.mock import AsyncMock
>>> inspect.signature(AsyncMock())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/karthikeyan/stuff/python/cpython/Lib/inspect.py", line 3272, in signature
    return Signature.from_callable(obj, follow_wrapped=follow_wrapped,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/karthikeyan/stuff/python/cpython/Lib/inspect.py", line 3020, in from_callable
    return _signature_from_callable(obj, sigcls=cls,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/karthikeyan/stuff/python/cpython/Lib/inspect.py", line 2507, in _signature_from_callable
    return _signature_from_function(sigcls, obj,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/karthikeyan/stuff/python/cpython/Lib/inspect.py", line 2351, in _signature_from_function
    positional = arg_names[:pos_count]
                 ~~~~~~~~~^^^^^^^^^^^^
TypeError: 'Mock' object is not subscriptable
>>> 
(myenv) ➜  cpython git:(main) git log Lib/unittest/mock.py 
(myenv) ➜  cpython git:(main) git checkout 4261b6bffc0b8bb5c6d4d80578a81b7520f4aefc~1 Lib/unittest/mock.py
Updated 1 path from ec0ed6ea8a
(myenv) ➜  cpython git:(main) ✗ ./python                                                                    
Python 3.12.0a0 (heads/main:575f8880bf, Aug 23 2022, 19:59:51) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import inspect
>>> from unittest.mock import AsyncMock
>>> inspect.signature(AsyncMock())
<Signature (*args, **kwargs)>

pythongh-96127: Fix `inspect.signature` call on mocks

@graingert

@graingert yes, your link was very useful. Please, take a look at my proposed soultion :)

@sobolevn

@sobolevn - where is your proposed solution?

@sobolevn

@sobolevn - where is your proposed solution?

gh-96127: Fix inspect.signature call on mocks #96335

pythongh-96127: Fix `inspect.signature` call on mocks

gh-96127: Fix `inspect.signature` call on mocks (#96335)

Looks like this has been fixed, thanks all!

I'm on 3.11.1 and this is happening.

    def _signature_from_function(cls, func, skip_bound_arg=True,
                                 globals=None, locals=None, eval_str=False):
        """Private helper: constructs Signature for the given python function."""
    
        is_duck_function = False
        if not isfunction(func):
            if _signature_is_functionlike(func):
                is_duck_function = True
            else:
                # If it's not a pure Python function, and not a duck type
                # of pure function:
                raise TypeError('{!r} is not a Python function'.format(func))
    
        s = getattr(func, "__text_signature__", None)
        if s:
            return _signature_fromstr(cls, func, s, skip_bound_arg)
    
        Parameter = cls._parameter_cls
    
        # Parameter information.
        func_code = func.__code__
        pos_count = func_code.co_argcount
        arg_names = func_code.co_varnames
        posonly_count = func_code.co_posonlyargcount
>       positional = arg_names[:pos_count]
E       TypeError: 'Mock' object is not subscriptable

This commit is present on main branch and 3.12 latest alpha. I guess this is not backported.

Workaround:

from inspect import signature
from unittest.mock import AsyncMock, MagicMock

temp_mock = AsyncMock()
mock = MagicMock(return_value=temp_mock())
signature(mock)

@sobolevn

@sobolevn should the PR be backported to 3.11?

pythongh-96127: Fix `inspect.signature` call on mocks (python#96335)

@sobolevn

@sobolevn ping?

[3.11] gh-96127: Fix `inspect.signature` call on mocks (#96335) (#101646

@mdczaplicki

@mdczaplicki @tirkarthi The backporting is done. The fix will be available in 3.11.3 ~~and 3.10.11~~ this April.

Fixed by gh-96335.

@arhadthedev

The fix will be available in 3.11.3 and 3.10.11 this April.

@arhadthedev where is the 3.10 backport?

I confused it with my other issue that was backported to both versions. Thank you for pointing out, edited.

pythongh-96127: Fix `inspect.signature` call on mocks (python#96335)

GH-108652 is a backport of this pull request to the 3.10 branch.

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Calling inspect.signature with an AsyncMock instance raises an exception #96127

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Calling inspect.signature with an AsyncMock instance raises an exception #96127

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Bug report

Your environment

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graingert commented on Aug 23, 2022

tirkarthi commented on Aug 23, 2022

sobolevn commented on Aug 27, 2022

cjw296 commented on Jan 3, 2023

AlexWaygood commented on Jan 3, 2023

hauntsaninja commented on Jan 20, 2023

mdczaplicki commented on Feb 7, 2023

tirkarthi commented on Feb 7, 2023

mdczaplicki commented on Feb 7, 2023

arhadthedev commented on Feb 7, 2023

4 remaining items

arhadthedev commented on Feb 8, 2023

arhadthedev commented on Feb 8, 2023

arhadthedev commented on Feb 8, 2023

AlexWaygood commented on Feb 8, 2023

arhadthedev commented on Feb 8, 2023

bedevere-bot commented on Aug 29, 2023

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