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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 getlayer(self, cls, nb=1, _track=None):
 """Return the nb^th layer that is an instance of cls."""

        if type(cls) is int:
            nb = cls+1
            cls = None
        if type(cls) is str and "." in cls:
            ccls,fld = cls.split(".",1)
        else:
            ccls,fld = cls,None
        if cls is None or self.__class__ == cls or self.__class__.name == ccls:
            if nb == 1:
                if fld is None:
                    return self
                else:
                    return self.getfieldval(fld)
            else:
                nb -=1
        for f in self.packetfields:
            fvalue_gen = self.getfieldval(f.name)
            if fvalue_gen is None:
                continue
            if not f.islist:
                fvalue_gen = SetGen(fvalue_gen,_iterpacket=0)
            for fvalue in fvalue_gen:
                if isinstance(fvalue, Packet):
                    track=[]
                    ret = fvalue.getlayer(cls, nb, _track=track)
                    if ret is not None:
                        return ret
                    nb = track[0]
        return self.payload.getlayer(cls,nb,_track=_track)