BUG: Update FutureWarning message to be more clear #55066
Description
Pandas version checks
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I have confirmed this bug exists on the latest version of pandas.
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I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
import pandas as pd
df = pd.DataFrame({"ID": [1,1,2,2,3],"B": [1,10,5,5,3]})
df_new = df[df.groupby(["ID"])["B"].transform(max) == df["B"]]Issue Description
This isn't necessarily a bug, but the other issue categories didn't fit it either.
In #53974, the use of built-in callable functions for SeriesGroupBy.transform()was deprecated. The current FutureWarning message that is displayed is:
E FutureWarning: The provided callable <built-in function max> is currently using SeriesGroupBy.max. In a future version of pandas, the provided callable will be used directly. To keep current behavior pass 'max' instead.
/pandas/core/apply.py:1828: FutureWarning
While the change is reasonable, I think the warning message could be updated to better convey the message. When I first saw the warning message, I didn't realize what was wrong. Obviously using the built-in functions was no longer supported, but the message said to keep current behavior pass 'max' instead, however this is exactly what I was doing, but I was passing the callable max instead.
After some time of reading the release notes and documentation, I realized the warning message was referring to the string "max".
Expected Behavior
My proposal is to just update the FutureWarning produced from this to explicitly state a string should be passed. Updating
FutureWarning: .... To keep current behavior pass 'max' instead.
to
FutureWarning: .... To keep current behavior pass the string 'max' instead.
Installed Versions
2.1.0