def parse_header_part(self, data):
packet_length = data[<NUM_LIT:0>]<EOL>packet_type = data[<NUM_LIT:1>]<EOL>packet_subtype = data[<NUM_LIT:2>]<EOL>sequence_number = data[<NUM_LIT:3>]<EOL>return {<EOL>'<STR_LIT>': packet_length,<EOL>'<STR_LIT>': packet_type,<EOL>'<STR_LIT>': self.PACKET_TYPES.get(packet_type),<EOL>'<STR_LIT>': packet_subtype,<EOL>'<STR_LIT>': self.PACKET_SUBTYPES.get(packet_subtype),<EOL>'<STR_LIT>': sequence_number<EOL>}<EOL>
Extracts and converts the RFX common header part of all valid
        packets to a plain dictionary. RFX header part is the 4 bytes prior
        the sensor vendor specific data part.

        The RFX common header part contains respectively:
        - packet length
        - packet type
        - packet sub-type
        - sequence number

        :param data: bytearray of received data
        :type data: bytearray