Empty Categorical has float dtype for .categories · Issue #17248 · pandas-dev/pandas (original) (raw)

It'd be more consistent if this had object dtype (and so an Index([]) instead of a Float64Index([]).

In [4]: pd.Categorical([]).categories.dtype Out[4]: dtype('float64')

I suspect this is just an implementation detail, not intentional.
Came up in #17236 (my rework to remove the keyword).