server_start_server.py

import socket
import threading

##### GUI component omitted #######
### See https://gist.github.com/effiongcharles/9d0d4fa3163b3350f1399902058fb9ae.js for preceeing source codes

server = None
HOST_ADDR = "0.0.0.0"
HOST_PORT = 8080
client_name = " "
clients = []
clients_names = []


# Start server function
def start_server():
    global server, HOST_ADDR, HOST_PORT # code is fine without this
    btnStart.config(state=tk.DISABLED)
    btnStop.config(state=tk.NORMAL)

    server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server.bind((HOST_ADDR, HOST_PORT))
    server.listen(5)  # server is listening for client connection

    threading._start_new_thread(accept_clients, (server, " "))

    lblHost["text"] = "Host: " + HOST_ADDR
    lblPort["text"] = "Port: " + str(HOST_PORT)