mock uses incorrect signature for partial and partialmethod with autospec #79644

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1. tirkarthi commented on Dec 11, 2018

   

   tirkarthi

   on Dec 11, 2018

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   This is a bug report for https://bugs.python.org/issue17185#msg331149 that I was asked to raise as a separate issue.

   1. When we call create_autospec it calls _get_signature_object that gets the signature for the given parameter. With functools.partial it returns a partial object and hence while getting the signature it returns the signature for the constructor of partial instead of the underlying function passed to functools.partial. I think a check needs to be added to make sure not to use func.__init__ when it's a partial object.

   2. When we call create_autospect on a class that has a partialmethod the self parameter is not skipped in the signature and thus it creates a signature with self causing error. The fix would be to handle partialmethod also in _must_skip that determines whether to skip self or not.

   Sample reproducer :

   from functools import partial, partialmethod
   from unittest.mock import create_autospec
   import inspect
   
   def foo(a, b):
       pass
   
   p = partial(foo, 1)
   m = create_autospec(p)
   m(1, 2, 3) # passes since signature is set as (*args, **kwargs) the signature of functools.partial constructor. This should throw TypeError under autospec
   
   
   class A:
   
       def f(self, a, b):
           print(a, b)
   
       g = partialmethod(f, 1)
   
   m = create_autospec(A)
   m().g(1, 2) # passes since signature is set as (self, b) and self is not skipped in _must_skip thus self=1, b=2. This should throw TypeError under autospec since the valid call is m().g(2)
2. tirkarthi

   added

   3.7 (EOL)end of lifeend of life

   3.8 (EOL)end of lifeend of life

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Dec 11, 2018
3. ezio-melotti

   transferred this issue fromon Apr 10, 2022
4. serhiy-storchaka

   added this to Unittest & doctest issueson May 20, 2022
5. claudiubelu

   added a commit that references this issue on Sep 21, 2026

   pythongh-79644: Fix create_autospec signature handling for functools …

   ...

   472f526
6. claudiubelu

   added a commit that references this issue on Oct 28, 2026

   pythongh-79644: Fix create_autospec signature handling for functools …

   ...

   8c1db00