BUG: Not properly checking if post_processing function is callable or not in _get_cythonized_result() function in class GroupBy

[KenilMehta]

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

Problem description

While looking at the code, I found this line which I think is a bug. In the current master branch, pandas/core/groupby/groupby.py file, in the _get_cythonized_result() function :

        if post_processing:
            if not callable(pre_processing):
                raise ValueError("'post_processing' must be a callable!")

While checking if post_processing is callable or not, we are actually passing pre_processing object instead of post_processing. This looks like a bug.

Expected Code

        if post_processing:
            if not callable(post_processing):
                raise ValueError("'post_processing' must be a callable!")

[jreback]

user codes don’t hit this
so is there any user facing issue?

[KenilMehta]

No, not that I know of.
But I think we should still fix it.

[jreback]

not averse to an AssertionError

[WillAyd]

Looks like a typo. PR welcome

[TomAugspurger]

@rhshadrach was this closed by #34372?

[rhshadrach]

@TomAugspurger - Yes, thanks for catching this.