def METHOD_NAME(self, service, level, seq):
    if service not in self.services:
        raise UnknownService()
    # compute the number of different launcher for this service in the runlevel
    l = []
    for _seq in self.services[service]:
        if self.services[service][_seq][level] != "none":
            l.append(self.services[service][_seq][level])
    if seq is None:
        if len(l) == 0:
            return "none"
        raise SeqError()
    if len(l) > 1:
        raise DupError()
    try:
        curstates = self.services[service][seq]
        curstate = curstates[int(level)]
    except:
        curstate = "none"
    if len(l) == 1 and curstate == "none":
        raise SeqError()
    return curstate