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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 _encode_msg(self, start_pos, offset, timestamp, key, value, attributes=0):
 """ Encode msg data into the `msg_buffer`, which should be allocated to at least the size of this message. """

        magic = self._magic
        buf = self._buffer
        pos = start_pos

        # Write key and value
        pos += self.KEY_OFFSET_V0 if magic == 0 else self.KEY_OFFSET_V1

        if key is None:
            struct.pack_into(">i", buf, pos, -1)
            pos += self.KEY_LENGTH
        else:
            key_size = len(key)
            struct.pack_into(">i", buf, pos, key_size)
            pos += self.KEY_LENGTH
            buf[pos: pos + key_size] = key
            pos += key_size

        if value is None:
            struct.pack_into(">i", buf, pos, -1)
            pos += self.VALUE_LENGTH
        else:
            value_size = len(value)
            struct.pack_into(">i", buf, pos, value_size)
            pos += self.VALUE_LENGTH
            buf[pos: pos + value_size] = value
            pos += value_size
        length = (pos - start_pos) - self.LOG_OVERHEAD

        # Write msg header. Note, that Crc will be updated later
        if magic == 0:
            self.HEADER_STRUCT_V0.pack_into(
                buf, start_pos,
                offset, length, 0, magic, attributes)
        else:
            self.HEADER_STRUCT_V1.pack_into(
                buf, start_pos,
                offset, length, 0, magic, attributes, timestamp)

        # Calculate CRC for msg
        crc_data = memoryview(buf)[start_pos + self.MAGIC_OFFSET:]
        crc = calc_crc32(crc_data)
        struct.pack_into(">I", buf, start_pos + self.CRC_OFFSET, crc)
        return crc