Unpack partial in iscoroutinefunction

[maximlt]

We've observed that inspect.iscoroutinefunction doesn't return the same output of different versions of Python 3.10 when the function is a functools.partial. We make sure that param's iscoroutinefunction (that covers async generators too) unpacks partials before checking if they wrap a coroutine/async generator or not.

• Before merging I would like to track down more precisely when things changed on CPython's side and if we see the same issue in Python 3.11 (if not, the unpacking could be removed when Python 3.10 support is dropped in some years), from memory we observed different results between CPython 3.10.5 and 3.10.13.

[maximlt]

import inspect
from functools import partial
import sys

print(sys.version)

class Foo:
    async def foo(self, x=None):
        return

cb = partial(Foo().foo, x=1)
print(inspect.iscoroutinefunction(cb))

# 3.10.5 | packaged by conda-forge | (main, Jun 14 2022, 07:05:37) [Clang 13.0.1 ]
# False

# 3.10.13 | packaged by conda-forge | (main, Oct 26 2023, 18:09:17) [Clang 16.0.6 ]
# True

I'm pretty sure this change occurred in python/cpython#94050. In our case f is not a method but a partial, that is unwrapped to a method, and a method is not a function so this used to return False. In the newer version with _signature_is_functionlike(f) that evaluates to True in our case the returned value is True. Anyway, what matters is that this has been backported to CPython 3.10 and 3.11, precisely to CPython 3.10.6 and 3.11.0 (backported before the actual release). So we could get rid of the partial unwrapping starting from Python 3.11.0.

def _has_code_flag(f, flag):
     while ismethod(f):
         f = f.__func__
     f = functools._unwrap_partial(f)
-    if not isfunction(f):
+    if not (isfunction(f) or _signature_is_functionlike(f)):
         return False
     return bool(f.__code__.co_flags & flag)