def asList(self):
        """ returns a Point value as a list of [x,y,<z>,<m>] """
        base = [self._x, self._y]
        if not self._z is None:
            base.append(self._z)
        elif not self._m is None:
            base.append(self._m)
        return base
returns a Point value as a list of [x,y,<z>,<m>]