def norm(self, x):
        """Calculate the norm of an element.

        This is the standard implementation using `inner`.
        Subclasses should override it for optimization purposes.

        Parameters
        ----------
        x1 : `LinearSpaceElement`
            Element whose norm is calculated.

        Returns
        -------
        norm : float
            The norm of the element.
        """
        return float(np.sqrt(self.inner(x, x).real))