与其在整个协议实现过程中混合决策逻辑，不如将它放在一个地方。
class DecisionProtocol(Protocol):
def connectionMade(self):
self.state = "undecided"
def makeProgressTowardsDecision(self, bytes):
# Do some stuff, eventually return ProtoA() or ProtoB()
def dataReceived(self, bytes):
if self.state == "undecided":
proto, extra = self.makeProgressTowardsDecision(bytes)
if proto is not None:
self.state = "decided"
self.decidedOnProtocol = proto
self.decidedOnProtocol.makeConnection(self.transport)
if extra:
self.decidedOnProtocol.dataReceived(extra)
else:
self.decidedOnProtocol.dataReceived(bytes)
def connectionLost(self, reason):
if self.state == "decided":
self.decidedOnProtocol.connectionLost(reason)
最终，您可以用更少的样板实现此目的：http ://tm.tl/3204/
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