Factory function for making unary operator methods for Factors.

def unary_operator(op):
    """
    Factory function for making unary operator methods for Factors.
    """
    # Only negate is currently supported.
    valid_ops = {'-'}
    if op not in valid_ops:
        raise ValueError("Invalid unary operator %s." % op)

    @with_doc("Unary Operator: '%s'" % op)
    @with_name(unary_op_name(op))
    def unary_operator(self):
        if self.dtype != float64_dtype:
            raise TypeError(
                "Can't apply unary operator {op!r} to instance of "
                "{typename!r} with dtype {dtypename!r}.\n"
                "{op!r} is only supported for Factors of dtype "
                "'float64'.".format(
                    op=op,
                    typename=type(self).__name__,
                    dtypename=self.dtype.name,
                )
            )

        # This can't be hoisted up a scope because the types returned by
        # unary_op_return_type aren't defined when the top-level function is
        # invoked.
        if isinstance(self, NumericalExpression):
            return NumExprFactor(
                "{op}({expr})".format(op=op, expr=self._expr),
                self.inputs,
                dtype=float64_dtype,
            )
        else:
            return NumExprFactor(
                "{op}x_0".format(op=op),
                (self,),
                dtype=float64_dtype,
            )
    return unary_operator