gh-131628: use duck-typing in inspect to support Cython

[tobiasdiez]

Currently, getfile and findsource are not able to return the correct source (file) for Cython methods since it uses isfunction which returns only true for true Python functions.

Here, we change this to a check for __code__ so that it works for Cython functions as well.

• Issue: Duck-typing in inspect.getfile #131628

[ghost]

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[sobolevn]

Thanks for the proposal, it needs tests in any case.

But, I am very concerned about the possible side-effects of this change.

[sobolevn]

This change can cause lots of problems to existing users. Because inspect is already used in quite complex code, which uses introspection of different objects in a very specific way.

[tobiasdiez]

There is no functional change in isfunction. I just thought it's good to clarify that only true Python functions are matched.

[sobolevn]

What about functions defined in PyPy, RustPython, and others? What about PyO3 functions? What about other possible binary ways of defining functions?

There is no functional change in isfunction

This would need a proof with real data, unfortunatelly :(

[tobiasdiez]

There is no functional change in isfunction
This would need a proof with real data, unfortunatelly :(

The github review interface might be confusing here: the only change in isfunction is in the docstring. The "real" change is in getfile and findsource.

[tobiasdiez]

Thanks for the proposal, it needs tests in any case.

I wasn't sure how to add a proper test. There doesn't seem to be any cython files in the repo. What I could do of course would be to create a dummy object with __code__ that is then recognized as a function.

But, I am very concerned about the possible side-effects of this change.

Could you please expand what kind of side-effects you would expect? Why would it lead to a problem if getfile(obj) returns obj.__code__.co_filename instead of erroring our if obj has a proper __code__?