BUG: ExponentialMovingWindow.agg/aggregate fails when passing a callable

[loicdiridollou]

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

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

import numpy as np
from pandas import DataFrame

df = DataFrame({"A": range(4, 8), "B": range(4)})

df.ewm(1).aggregate(sum)  # fails
df.ewm(1).aggregate("sum") # works
df.ewm(1).aggregate(np.sum) # fails

Issue Description

ExponentialMovingWindow.agg/aggregate fails when using a function (strings are fine).
Seems like there is an issue in how the aggregate call is wired, rolling does not suffer from the same issue (but any ExponentialGroupBy and alike will).
The traceback is the following:

  File "<python-input-15>", line 1, in <module>
    df.ewm(1).aggregate(np.sum) # fails
    ~~~~~~~~~~~~~~~~~~~^^^^^^^^
  File "/Users/loic.diridollou/Documents/Code/pandas-stubs/gh1641_pandas_30/.venv/lib/python3.14/site-packages/pandas/core/window/ewm.py", line 524, in aggregate
    return super().aggregate(func, *args, **kwargs)
           ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/loic.diridollou/Documents/Code/pandas-stubs/gh1641_pandas_30/.venv/lib/python3.14/site-packages/pandas/core/window/rolling.py", line 654, in aggregate
    return self.apply(func, raw=False, args=args, kwargs=kwargs)
           ^^^^^^^^^^
  File "/Users/loic.diridollou/Documents/Code/pandas-stubs/gh1641_pandas_30/.venv/lib/python3.14/site-packages/pandas/core/window/rolling.py", line 305, in __getattr__
    raise AttributeError(
        f"'{type(self).__name__}' object has no attribute '{attr}'"
    )
AttributeError: 'ExponentialMovingWindow' object has no attribute 'apply'. Did you mean: '_apply'?

Expected Behavior

The use of a callable should not fail since other functions passed as string (mean, cov, corr, sum, ...). are working fine.

Installed Versions

Details

Replace this line with the output of pd.show_versions()

[tendinginfinity24]

I tested this on the current main branch and can no longer reproduce the failure. Instead, I now get a FutureWarning indicating that callable dispatch currently maps to ExponentialMovingWindow.sum, and that in a future version the callable will be used directly.

/home/tendinginfinity/open_source/pandas/pandas/pandas/pytest.py:6: FutureWarning: The provided callable is currently using ExponentialMovingWindow.sum. In a future version of pandas, the provided callable will be used directly. To keep current behavior pass the string "sum" instead.
df.ewm(1).aggregate(sum) # fails
/home/tendinginfinity/open_source/pandas/pandas/pandas/pytest.py:8: FutureWarning: The provided callable <function sum at 0x7f784fce1940> is currently using ExponentialMovingWindow.sum. In a future version of pandas, the provided callable will be used directly. To keep current behavior pass the string "sum" instead.
df.ewm(1).aggregate(np.sum) # fails