Factory function for making binary operator methods on a Factor subclass.

    Returns a function, "binary_operator" suitable for implementing functions
    like __add__.

def binary_operator(op):
    """
    Factory function for making binary operator methods on a Factor subclass.

    Returns a function, "binary_operator" suitable for implementing functions
    like __add__.
    """
    # When combining a Factor with a NumericalExpression, we use this
    # attrgetter instance to defer to the commuted implementation of the
    # NumericalExpression operator.
    commuted_method_getter = attrgetter(method_name_for_op(op, commute=True))

    @with_doc("Binary Operator: '%s'" % op)
    @with_name(method_name_for_op(op))
    @coerce_numbers_to_my_dtype
    def binary_operator(self, other):
        # This can't be hoisted up a scope because the types returned by
        # binop_return_type aren't defined when the top-level function is
        # invoked in the class body of Factor.
        return_type = binop_return_type(op)
        if isinstance(self, NumExprFactor):
            self_expr, other_expr, new_inputs = self.build_binary_op(
                op, other,
            )
            return return_type(
                "({left}) {op} ({right})".format(
                    left=self_expr,
                    op=op,
                    right=other_expr,
                ),
                new_inputs,
                dtype=binop_return_dtype(op, self.dtype, other.dtype),
            )
        elif isinstance(other, NumExprFactor):
            # NumericalExpression overrides ops to correctly handle merging of
            # inputs.  Look up and call the appropriate reflected operator with
            # ourself as the input.
            return commuted_method_getter(other)(self)
        elif isinstance(other, Term):
            if self is other:
                return return_type(
                    "x_0 {op} x_0".format(op=op),
                    (self,),
                    dtype=binop_return_dtype(op, self.dtype, other.dtype),
                )
            return return_type(
                "x_0 {op} x_1".format(op=op),
                (self, other),
                dtype=binop_return_dtype(op, self.dtype, other.dtype),
            )
        elif isinstance(other, Number):
            return return_type(
                "x_0 {op} ({constant})".format(op=op, constant=other),
                binds=(self,),
                # .dtype access is safe here because coerce_numbers_to_my_dtype
                # will convert any input numbers to numpy equivalents.
                dtype=binop_return_dtype(op, self.dtype, other.dtype)
            )
        raise BadBinaryOperator(op, self, other)

    return binary_operator