Remove specified key and return all corresponding values.
        
        If they key is not found, an empty list is return.
        
        >>> m = MutableMultiMap([('a', 1), ('b', 2), ('b', 3), ('c', 4)])
        >>> m.popall('a')
        [1]
        >>> m.popall('b')
        [2, 3]
        >>> m.popall('x')
        []

def popall(self, key):
        """Remove specified key and return all corresponding values.
        
        If they key is not found, an empty list is return.
        
        >>> m = MutableMultiMap([('a', 1), ('b', 2), ('b', 3), ('c', 4)])
        >>> m.popall('a')
        [1]
        >>> m.popall('b')
        [2, 3]
        >>> m.popall('x')
        []
        
        """
        values = self.getall(key)
        try:
            del self[key]
        except KeyError:
            pass
        return values