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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 guess_cls(self):
 """Guess the packet class that must be used on the interface"""


        # Get the data link type
        try:
            ret = fcntl.ioctl(self.ins, BIOCGDLT, struct.pack('I', 0))
            ret = struct.unpack('I', ret)[0]
        except IOError:
            cls = conf.default_l2
            warning("BIOCGDLT failed: unable to guess type. Using %s !",
                    cls.name)
            return cls

        # Retrieve the corresponding class
        try:
            return conf.l2types[ret]
        except KeyError:
            cls = conf.default_l2
            warning("Unable to guess type (type %i). Using %s", ret, cls.name)