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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 transition(prior_state, next_state):
 """ Transitions to a non-standard state Raises InvalidStateTransition if next_state is not allowed. :param prior_state: <str> :param next_state: <str> :return: <str> """

    if next_state not in STATES[prior_state][TRANSITION]:
        acceptable = STATES[prior_state][TRANSITION]
        err = "cannot {}->{} may only {}->{}".format(prior_state,
                                                     next_state,
                                                     prior_state,
                                                     acceptable)
        raise InvalidStateTransition(err)
    return next_state