Appends C{obj} to this index.

        @note: Uniqueness is not checked
        @return: The reference to C{obj} in this index.

def append(self, obj):
        """
        Appends C{obj} to this index.

        @note: Uniqueness is not checked
        @return: The reference to C{obj} in this index.
        """
        h = self.func(obj)

        self.list.append(obj)
        idx = len(self.list) - 1
        self.dict[h] = idx

        return idx