def add(self, other):
        """Return the operator self + other.

        Args:
            other (Operator): an operator object.

        Returns:
            Operator: the operator self + other.

        Raises:
            QiskitError: if other is not an operator, or has incompatible
            dimensions.
        """
        if not isinstance(other, Operator):
            other = Operator(other)
        if self.dim != other.dim:
            raise QiskitError("other operator has different dimensions.")
        return Operator(self.data + other.data, self.input_dims(),
                        self.output_dims())
Return the operator self + other.

        Args:
            other (Operator): an operator object.

        Returns:
            Operator: the operator self + other.

        Raises:
            QiskitError: if other is not an operator, or has incompatible
            dimensions.