telnetlib_option_negotiation_callback_example.py

def option_negotiator(socket, command, option):
    # telnet really sucks, if you wanted more proof:
    if command in (DO, DONT):
        if command == DO and option == TTYPE: # "can you tell me your terminal type?"
            socket.sendall(IAC + WILL + TTYPE) # "of course I will! let's do a whole pointless subnegotiation!"
        else: # for all other commands just refuse
            socket.sendall(IAC + WONT + option)
    elif command in (WILL, WONT):
        if command == WILL and option == ECHO: # "I will echo all characters back to you"
            socket.sendall(IAC + DO + ECHO) # "yes please, echo all characters"
        else: # all other offers just reply with a "don't"
            socket.sendall(IAC + DONT + option)
    elif command == SE: # a subnegotiation has started (hopefully for terminal-type)
        if self.sock.sbdataq == TTYPE + chr(1): # reply with terminal-type, chr(1) = "SEND", chr(0) = "IS"
            socket.sendall(IAC + SB + TTYPE + chr(0) + 'vt220' + IAC + SE)