inspect.iscoroutinefunction / isgeneratorfunction / isasyncgenfunction can't handle partialmethod objects

[mjpieters]

BPO	38364
Nosy	@mjpieters, @asvetlov, @1st1, @Dreamsorcerer, @jalaziz
PRs	bpo-38364: unwrap partialmethods just like we unwrap partials #16600

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-10-03.13:28:44.060>
labels = ['3.8', 'type-bug', 'library', '3.9', '3.10']
title = "inspect.iscoroutinefunction / isgeneratorfunction / isasyncgenfunction can't handle partialmethod objects"
updated_at = <Date 2022-03-05.22:48:08.143>
user = 'https://github.com/mjpieters'

bugs.python.org fields:

activity = <Date 2022-03-05.22:48:08.143>
actor = 'jalaziz'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-10-03.13:28:44.060>
creator = 'mjpieters'
dependencies = []
files = []
hgrepos = []
issue_num = 38364
keywords = ['patch']
message_count = 2.0
messages = ['353849', '414598']
nosy_count = 5.0
nosy_names = ['mjpieters', 'asvetlov', 'yselivanov', 'dreamsorcerer', 'jalaziz']
pr_nums = ['16600']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38364'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[mjpieters]

This is a follow-up to bpo-33261, which added general support for detecting generator / coroutine / async generator functions wrapped in partials. It appears that partialmethod objects were missed out.

While a partialmethod object will produce a functools.partial() object on binding to an instance, the .func attribute of that partial is a bound method, not a function, and the current _has_code_flag implementation unwraps methods *before* it unwraps partials.

Next, binding to a class produces a partialmethod._make_unbound_method.._method wrapper function. _unwrap_partial can't unwrap this, as it doesn't handle this case; it could look for the _partialmethod attribute and follow that to find the .func attribute.

Test case:

import inspect
import functools

class Foo:
 async def bar(self, a): return a
 ham = partialmethod(bar, "spam")

print(inspect.iscoroutinefunction(Foo.bar) # True
print(inspect.iscoroutinefunction(Foo.ham) # False
instance = Foo()
print(inspect.iscoroutinefunction(instance.bar) # True
print(inspect.iscoroutinefunction(instance.ham) # False

[jalaziz]

I've recently ran into this via unittest.mock.patch.object. Mocking an asynchronous partial method returns MagicMock and not AsyncMagicMock, causing some pretty hard to debug failures.

[graingert]

see also #67707

[pavelm10]

The above test case slightly changed:

def test_dummy():
 import inspect
 import functools

 class Foo:
 async def bar(self, a): return a
 ham = functools.partialmethod(bar, "spam")

 assert inspect.iscoroutinefunction(Foo.bar) # True
 assert not inspect.iscoroutinefunction(Foo.ham) # False
 instance = Foo()
 assert inspect.iscoroutinefunction(instance.bar) # True
 assert inspect.iscoroutinefunction(instance.ham) # False

IS NOT failing for Python 3.10.7
IS failing for Python 3.10.2
Other 3.10.x not tested.

[mjpieters]

The above test case slightly changed:

 assert inspect.iscoroutinefunction(Foo.bar) # True
 assert not inspect.iscoroutinefunction(Foo.ham) # False

Why did you change the test to add not?