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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 in_port(self):
 """Retrieve the 'in_port' that generated the PacketIn. This method will look for the OXM_TLV with type OFPXMT_OFB_IN_PORT on the `oxm_match_fields` field from `match` field and return its value, if the OXM exists. Returns: The integer number of the 'in_port' that generated the PacketIn if it exists. Otherwise return None. """

        in_port = self.match.get_field(OxmOfbMatchField.OFPXMT_OFB_IN_PORT)
        return int.from_bytes(in_port, 'big')