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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _check_transition_id(self, transition):
 """Checks the validity of a transition id Checks whether the transition id is already used by another transition within the state :param rafcon.core.transition.Transition transition: The transition to be checked :return bool validity, str message: validity is True, when the transition is valid, False else. message gives more information especially if the transition is not valid """

        transition_id = transition.transition_id
        if transition_id in self.transitions and transition is not self.transitions[transition_id]:
            return False, "transition_id already existing"
        return True, "valid"