[issue36880] Returning None from a callback with restype py_object decrements None's refcount too much

[dgelessus]

dgelessus <dgelessus+bugs.python.org at me.com> added the comment:

Thank you for looking into this! I can confirm that Eryk Sun's change fixes the issue for me locally.

I'm up for making the patch for this. Regarding tests, I see there are already some refcount-related ctypes tests in Lib/ctypes/test/test_refcounts.py - should I add another test case there that reproduces this situation and ensures that None's refcount is unaffected? (I imagine testing against None's refcount will be a bit fragile, so it might be best to call the previously-buggy function in a loop and check afterwards that None's refcount hasn't changed significantly.)

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<https://bugs.python.org/issue36880>
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