<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def list_images(self, image_state):
 """Returns the list of the images in the Cloud. in image_state of type :class:`CloudImageState` out return_names of type str Images names. return return_ids of type str Images ids. """

        if not isinstance(image_state, CloudImageState):
            raise TypeError("image_state can only be an instance of type CloudImageState")
        (return_ids, return_names) = self._call("listImages",
                     in_p=[image_state])
        return (return_ids, return_names)