A simple TCP listener that echoes what you send it. Works in Python 3 and 2. Based on the python2 listener in Black Hat Python.

echo9999.py

#!/usr/env/python
from __future__ import print_function
import socket
import threading

bind_ip = "127.0.0.1"
bind_port = 9999
server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

server.bind((bind_ip,bind_port))
server.listen(5)
print("[*] Listening on %s:%d" % (bind_ip,bind_port))

# this is our client-handling thread
def handle_client(client_socket):
    # print out what the client sends
    request = client_socket.recv(1024)
    print("[*] Received: %s" % request)

    # send back a packet
    client_socket.send(b"ACK!\n"+request)
    client_socket.close()

while True:
    client,addr = server.accept()
    print("[*] Accepted connection from: %s:%d" % (addr[0],addr[1]))
    # spin up our client thread to handle incoming data
    client_handler = threading.Thread(target=handle_client,args=(client,))
    client_handler.start()