str.cat inconsistent for CategoricalIndex

[h-vetinari]

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')

[WillAyd]

Why wouldn't you just rename your categories?

[h-vetinari]

@WillAyd
this was just a toy example - if there's more to concatenate, it gets more unwieldy. But more than that, it makes no sense that a.str.cat(b) works, but b.str.cat(a) doesn't.