Returns the unique string representation of the number.

def repr(self, *args, **kwargs):
        """
        Returns the unique string representation of the number.
        """
        if not self.is_numpy:
            text = "'" + self.str(*args, **kwargs) + "'"
        else:
            text = "{} numpy array, {} uncertainties".format(self.shape, len(self.uncertainties))

        return "<{} at {}, {}>".format(self.__class__.__name__, hex(id(self)), text)