str.cat inconsistent for CategoricalIndex #20842
Description
The str.cat-accessor works for CategoricalIndex as target, but not as caller. This is inconsistent.
a = pd.Index(['a', 'b', 'a']) b = pd.Index(['a', 'b', 'a'], dtype='category') a.str.cat(b) # Index(['aa', 'bb', 'aa'], dtype='object') b.str.cat(a) # AttributeError: Can only use .str accessor with string values (i.e. inferred_type is 'string', 'unicode' or 'mixed')