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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 inv_endianness(pkt):
 """ Invert the order of the first four bytes of a CAN packet This method is meant to be used specifically to convert a CAN packet between the pcap format and the socketCAN format :param pkt: str of the CAN packet :return: packet str with the first four bytes swapped """

        len_partial = len(pkt) - 4  # len of the packet, CAN ID excluded
        return struct.pack('<I{}s'.format(len_partial),
                           *struct.unpack('>I{}s'.format(len_partial), pkt))