REF: avoid getattr pattern in libgroupby rank functions

[jbrockmendel]

cc @WillAyd do we need to do anything special w/r/t the comment on L1220 re #19560?

[gfyoung]

Are these just unused?

[jbrockmendel]

If you look at get_cython_function in groupby.ops, you'll see we do a thing with checking for libgroupby func_name and then libgroupby.func_name_dtype. This pattern was put in place back before we started using fused types for libgroupby, and now cython effectively choose the correct func_name_dtype for us when we just use func_name

[WillAyd]

cc @WillAyd do we need to do anything special w/r/t the comment on L1220 re #19560?

Is this changing behavior when trying to rank objects? I think on master raises an error

>>> pd.DataFrame([[1]], dtype=object).groupby([1]).rank()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/williamayd/clones/pandas/pandas/core/groupby/groupby.py", line 2144, in rank
    axis=axis,
  File "/Users/williamayd/clones/pandas/pandas/core/groupby/groupby.py", line 867, in _cython_transform
    result, _ = self.grouper.transform(obj.values, how, **kwargs)
  File "/Users/williamayd/clones/pandas/pandas/core/groupby/ops.py", line 621, in transform
    return self._cython_operation("transform", values, how, axis, **kwargs)
  File "/Users/williamayd/clones/pandas/pandas/core/groupby/ops.py", line 583, in _cython_operation
    result, values, labels, func, is_numeric, is_datetimelike, **kwargs
  File "/Users/williamayd/clones/pandas/pandas/core/groupby/ops.py", line 658, in _transform
    transform_func(result, values, comp_ids, ngroups, is_datetimelike, **kwargs)
  File "/Users/williamayd/clones/pandas/pandas/core/groupby/ops.py", line 441, in wrapper
    return f(afunc, *args, **kwargs)
  File "/Users/williamayd/clones/pandas/pandas/core/groupby/ops.py", line 393, in <lambda>
    kwargs.get("na_option", "keep"),
TypeError: 'NoneType' object is not callable

Though not sure how well tested that is. Ideally would be explicitly disallowed but looks like that PR is still open, so might want to be careful when changing this

[jbrockmendel]

Is this changing behavior when trying to rank objects? I think on master raises an error

The same example now raises pandas.core.base.DataError: No numeric types to aggregate

[jreback]

thanks @jbrockmendel