def popitem(self):
        u"""*x.popitem() → (k, v)*

        Remove and return some item as a (key, value) pair.

        :raises KeyError: if *x* is empty.
        """
        if not self:
            raise KeyError('mapping is empty')
        key, val = self._fwdm.popitem()
        del self._invm[val]
        return key, val
u"""*x.popitem() → (k, v)*

        Remove and return some item as a (key, value) pair.

        :raises KeyError: if *x* is empty.