'mode' not recognized by df.groupby().agg(), but pd.Series.mode works

This works:

df = pd.DataFrame({'A': [1, 2, 1, 2, 1, 2, 3], 'B': [1, 1, 1, 2, 2, 2, 2]})
df.groupby('B').agg(pd.Series.mode)

but this doesn’t:

df.groupby('B').agg('mode')

...
AttributeError: Cannot access callable attribute 'mode' of 'DataFrameGroupBy' objects, try using the 'apply' method

I thought all the series aggregate methods propagated automatically to groupby, but I’ve probably misunderstood?

[kernc]

What about when grouping Series?

I have no issue with .agg('mode') returning the first mode, if any, while issuing a warning if the modes were multuple.

[gosuto-inzasheru]

I encountered this problem and ended up settling for this: .agg({'column': lambda x: pd.Series.mode(x)[0][0]})

But yes, I agree with @kernc, I would not mind .agg('mode') returning the first mode if multiple modes are returned.