Patched async function not registering calls until coroutine is awaited

[GabrielSalla]

Bug report

Bug description:

When using autospec=True the patched async function only has calls registered after the coroutine is awaited. This behavior started happening after I upgraded from 3.12 to 3.13.6.

Code to reproduce

File tests/other_module.py

async def a(value):
 return value * 2

File tests/test_1.py

from unittest.mock import patch

import pytest

import other_module

pytestmark = pytest.mark.asyncio(loop_scope="session")

def b(value):
 return other_module.a(value)


async def test_1():
 with patch.object(other_module, "a", side_effect=other_module.a, autospec=True) as a_mock:
 result = b(10)

 assert not a_mock.called # This should be True because 'a' was called, but it's False

 await result
 assert a_mock.called # Now it's True

CPython versions tested on:

3.13

Operating systems tested on:

Linux

[corona10]

cc @kumaraditya303

[kumaraditya303]

This behavior started happening after I upgraded from 3.12 to 3.13.6.

Can you do git bisect to find which commit caused the change in behavior?

[tirkarthi]

This seems to be a regression with 9bf8d82 where async def is used instead of def to help inspect.iscoroutinefunction . create_autospec should check for signature as per docs despite the function being async as per the docs. Since the change was in Python 3.13 and not backported maybe set the signature as sync and mark it using markcoroutinefunction introduced in Python 3.12 but this might be an issue with mock backport since inspect will not have markcoroutinefunction.

https://docs.python.org/3/library/inspect.html#inspect.markcoroutinefunction

https://docs.python.org/3/library/unittest.mock.html#unittest.mock.create_autospec

unittest.mock.create_autospec(spec, spec_set=False, instance=False, **kwargs)
Create a mock object using another object as a spec. Attributes on the mock will use the corresponding attribute on the spec object as their spec.
Functions or methods being mocked will have their arguments checked to ensure that they are called with the correct signature.

# gh137594_autospec

from unittest.mock import create_autospec

async def a(b, c):
 pass

spec = create_autospec(a)
spec()

Before 9bf8d82

python gh137594_autospec.py
Traceback (most recent call last):
 File "/home/karthikeyan/stuff/python/gh137594/gh137594_autospec.py", line 7, in <module>
 spec()
 ~~~~^^
 File "<string>", line 2, in a
 File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/mock.py", line 192, in checksig
 sig.bind(*args, **kwargs)
 ~~~~~~~~^^^^^^^^^^^^^^^^^
 File "/home/karthikeyan/stuff/python/cpython/Lib/inspect.py", line 3233, in bind
 return self._bind(args, kwargs)
 ~~~~~~~~~~^^^^^^^^^^^^^^
 File "/home/karthikeyan/stuff/python/cpython/Lib/inspect.py", line 3146, in _bind
 raise TypeError(msg) from None
TypeError: missing a required argument: 'b'

main as of c919d02

python gh137594_autospec.py
/home/karthikeyan/stuff/python/gh137594/gh137594_autospec.py:7: RuntimeWarning: coroutine 'a' was never awaited
 spec()
RuntimeWarning: Enable tracemalloc to get the object allocation traceback

A simpler reproducer for the issue without pytest dependency

import asyncio
from unittest.mock import patch
import other_module


async def a(i):
 pass

async def a1(i):
 pass

def b(value):
 return a(value)


async def test_1():
 with patch(f"{__name__}.a", side_effect=a1, autospec=True) as a_mock:
 result = b(10)

 assert a_mock.called # This should be True because 'a' was called, but it's False

 await result
 assert a_mock.called # Now it's True


asyncio.run(test_1())

cc: @graingert @cjw296

[cjw296]

@tirkarthi - nice work on the investigation. Would your reproducer be something we can add as a unit test to prevent this happening again? If so, then the fix becomes getting that test to pass while still keeping the test(s) introduced in #94962 passing.

I'm not sure I understand the fix you're proposing, but if you could put it and the unit test in a new PR that would be a great place to start. The backport is a secondary concern...

[tirkarthi]

If so, then the fix becomes getting that test to pass while still keeping the test(s) introduced in #94962 passing.

My patch will need a change to the tests since #94962 explicitly has a test so that a coroutine function can be called with invalid signature and the validation is done only when it's awaited unlike the normal flow and in previous versions of python where the signature validation is during the call to coroutine function itself instead of during await. With autospec I would expect the validation to be done during the call itself.

Relevant test : https://github.com/python/cpython/pull/94962/files#diff-701e692796f7bc8001aec6f354f4770ad9fdf05116ca6934fc1dbf7705f80fdbR251-R252

Python 3.11 vs main difference

python3.11 -m asyncio 
asyncio REPL 3.11.11 (main, Dec 4 2024, 08:55:08) [GCC 9.4.0] on linux
Use "await" directly instead of "asyncio.run()".
Type "help", "copyright", "credits" or "license" for more information.
>>> import asyncio
>>> async def foo(a, b): pass
... 
>>> foo()
Traceback (most recent call last):
 File "/usr/lib/python3.11/concurrent/futures/_base.py", line 456, in result
 return self.__get_result()
 ^^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.11/concurrent/futures/_base.py", line 401, in __get_result
 raise self._exception
 File "/usr/lib/python3.11/asyncio/__main__.py", line 34, in callback
 coro = func()
 ^^^^^^
 File "<console>", line 1, in <module>
TypeError: foo() missing 2 required positional arguments: 'a' and 'b'
>>> from unittest.mock import create_autospec
>>> mock = create_autospec(foo)
>>> mock()
Traceback (most recent call last):
 File "/usr/lib/python3.11/concurrent/futures/_base.py", line 456, in result
 return self.__get_result()
 ^^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.11/concurrent/futures/_base.py", line 401, in __get_result
 raise self._exception
 File "/usr/lib/python3.11/asyncio/__main__.py", line 34, in callback
 coro = func()
 ^^^^^^
 File "<console>", line 1, in <module>
 File "<string>", line 2, in foo
 File "/usr/lib/python3.11/unittest/mock.py", line 192, in checksig
 sig.bind(*args, **kwargs)
 File "/usr/lib/python3.11/inspect.py", line 3195, in bind
 return self._bind(args, kwargs)
 ^^^^^^^^^^^^^^^^^^^^^^^^
 File "/usr/lib/python3.11/inspect.py", line 3110, in _bind
 raise TypeError(msg) from None
TypeError: missing a required argument: 'a'

main branch where invalid signature is not validated during call time.

./python -m asyncio 
asyncio REPL 3.15.0a0 (heads/main:d2deb8fdef1, Oct 9 2025, 18:30:25) [GCC 9.4.0] on linux
Use "await" directly instead of "asyncio.run()".
Type "help", "copyright", "credits" or "license" for more information.
>>> import asyncio
>>> async def foo(a, b): pass
... 
>>> foo()
Traceback (most recent call last):
 File "/home/karthikeyan/stuff/python/cpython/Lib/concurrent/futures/_base.py", line 450, in result
 return self.__get_result()
 ~~~~~~~~~~~~~~~~~^^
 File "/home/karthikeyan/stuff/python/cpython/Lib/concurrent/futures/_base.py", line 395, in __get_result
 raise self._exception
 File "/home/karthikeyan/stuff/python/cpython/Lib/asyncio/__main__.py", line 44, in callback
 coro = func()
 File "<python-input-1>", line 1, in <module>
 foo()
 ~~~^^
TypeError: foo() missing 2 required positional arguments: 'a' and 'b'
>>> from unittest.mock import create_autospec
>>> mock = create_autospec(foo)

# mock() is allowed and signature is validated only during await
>>> m = mock()
>>> await m
Traceback (most recent call last):
 File "/home/karthikeyan/stuff/python/cpython/Lib/concurrent/futures/_base.py", line 450, in result
 return self.__get_result()
 ~~~~~~~~~~~~~~~~~^^
 File "/home/karthikeyan/stuff/python/cpython/Lib/concurrent/futures/_base.py", line 395, in __get_result
 raise self._exception
 File "<python-input-6>", line 1, in <module>
 await m
 File "<string>", line 2, in foo
 File "/home/karthikeyan/stuff/python/cpython/Lib/unittest/mock.py", line 218, in checksig
 sig.bind(*args, **kwargs)
 ~~~~~~~~^^^^^^^^^^^^^^^^^
 File "/home/karthikeyan/stuff/python/cpython/Lib/inspect.py", line 3233, in bind
 return self._bind(args, kwargs)
 ~~~~~~~~~~^^^^^^^^^^^^^^
 File "/home/karthikeyan/stuff/python/cpython/Lib/inspect.py", line 3146, in _bind
 raise TypeError(msg) from None
TypeError: missing a required argument: 'a'