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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 find_tendril(cls, proto, addr):
 """ Finds the tendril corresponding to the protocol and address tuple. Returns the Tendril object, or raises KeyError if the tendril is not tracked. The address tuple is the tuple of the local address and the remote address for the tendril. """


        # First, normalize the proto
        proto = proto.lower()

        # Now, find and return the tendril
        return cls._tendrils[proto][addr]