Index.add OK but sub not? (original) (raw)

Curious about why Index.__add__ tries does the natural thing but Index.__sub__ raises TypeError.

    def __add__(self, other):
        return Index(np.array(self) + other)

    def __radd__(self, other):
        return Index(other + np.array(self))

    __iadd__ = __add__

    def __sub__(self, other):
        raise TypeError("cannot perform __sub__ with this index type: "
                        "{typ}".format(typ=type(self)))