python send/receive hex data via TCP socket

问题:

I have a ethenet access control device that is said to be able to communicate via TCP.
How can i send a pachet by entering the HEX data, since this is what i have from their manual (a standard format for the communication packets sent and received after each command)
Can you please show some example code or links to get started....

standard return packet from the terminal
                               Size (bytes) 
BS (0x08) : ASCII Character         1
STX (0x02) : ASCII Character        1 
LENGTH : length from BS to ETX      4 
TID : system unique I.D.            1 
RESULT                              1 
DATA : returned parameter           N 
CHECKSUM : byte sum from BS to DATA 1 
ETX (0x03) : ASCII Character        1 

Standard command packet to the terminal  
                               Size (bytes) 
ACK (0x06) : ASCII Character         1 
STX (0x02) : ASCII Character         1 
LENGTH : length from ACK to ETX      4 
TID : system unique I.D. (ex: 1)     1 
COMMAND                              1 
Access Key(Optional)                 6 
DATA : command parameter             N 
CHECKSUM : byte sum from ACK to DATA 1 
ETX (0x03) : ASCII Character         1 

This packet starts from ACK. 
In this packet, multiple byte value must be started from MSB. 
For example, if length was 10, LENGTH is 0x00 0x00 0x00 0x0a. 

回答1:

I'd use struct.pack to prepare the string of bytes to send, from the data you want to send. Be sure to start the packing format with > to mean you want big-endian ordering and standard sizes, since they document that so clearly!

So (I don't know what the "optional" means for the access key, I'll assume it means that the field can be all-zero bytes if you have no access key), if "data" is already a string of bytes and "command" a small unsigned integer for example, something like...:

def stringfor(command, data, accesskey='\0'*6, tid=1):
  length = 16 + len(data)
  prefix = struct.pack('>BBIBB6s', 6, 2, length, tid, command, accesskey)
  checksum = sum(ord(c) for c in prefix) &0xFF
  return prefix + chr(checksum) + chr(3)

回答2:

Just encode the hex data in a string:

'\x34\x82\xf6'