def norm(self, x):
        """Return the norm of ``x``.

        Parameters
        ----------
        x : `LinearSpaceElement`
            Element whose norm to compute.

        Returns
        -------
        norm : float
            Norm of ``x``.
        """
        if x not in self:
            raise LinearSpaceTypeError('`x` {!r} is not an element of '
                                       '{!r}'.format(x, self))
        return float(self._norm(x))