subscribeLeader(string, double) -> None

        Subscribe for the leading vehicle id together with the distance.
        The dist parameter defines the maximum lookahead, 0 calculates a lookahead from the brake gap.

def subscribeLeader(self, vehID, dist=0., begin=0, end=2**31 - 1):
        """subscribeLeader(string, double) -> None

        Subscribe for the leading vehicle id together with the distance.
        The dist parameter defines the maximum lookahead, 0 calculates a lookahead from the brake gap.
        """
        self._connection._subscribe(tc.CMD_SUBSCRIBE_VEHICLE_VARIABLE, begin, end, vehID,
                                    (tc.VAR_LEADER,), {tc.VAR_LEADER: struct.pack("!Bd", tc.TYPE_DOUBLE, dist)})