code: def key_changes(self, from_token, to_token):
          
          params = {"from": from_token, "to": to_token}
          return self._send("GET", "/keys/changes", query_params=params)
docs: Gets a list of users who have updated their device identity keys.
  
          Args:
              from_token (str): The desired start point of the list. Should be the
                  next_batch field from a response to an earlier call to /sync.
              to_token (str): The desired end point of the list. Should be the next_batch
                  field from a recent call to /sync - typically the most recent such call.