May you help $,$ users can not communicate with each ohter, may you also improve my code?

server:

import socket import threading import os # Folder for shared files shared$\_$folder $=$ os$.$environ.get$("$SERVER$\_$SHARED$\_$FILES", "SharedFiles"$)$ # Global variables for clients and usernames clients $=\{\}$ usernames $=\{\}$ def handle$\_$client$($conn$,$ addr$)$: print$($f$"$New connection from $\{$addr$\}")$ username $=$ conn.recv$(1024).$decode$()$ if username: usernames$[$conn$]=$ username broadcast$($f$"[\{$username$\}]$ has joined", conn$)$ clients$[$conn$]=$ addr try: while True: message $=$ conn.recv$(1024).$decode$()$ if message: if message.startswith$("/$exit$")$: disconnect$\_$client$($conn$)$ break elif message.startswith$("/$broadcast$")$: broadcast$($f$"[\{$username$\}]$: $\{$message$[10$:$]\}",$ conn$)$ elif message.startswith$("/$unicast$")$: target$\_$user, msg $=$ message.split$(\text{'}\text{'},2)[1$:$]$ send$\_$to$\_$user$($target$\_$user, f$"[\{$username$\}]$: $\{$msg$\}")$ elif message.startswith$("/$files$")$: list$\_$files$($conn$)$ elif message.startswith$("/$download$")$: filename $=$ message.split$(\text{'}\text{'},1)[1]$ send$\_$file$($conn$,$ filename$)$ else: conn.send$("$Invalid command.".encode$())$ except Exception as e: print$($f$"$Error with $\{$username$\}$: $\{$e$\}")$ finally: disconnect$\_$client$($conn$)$ def broadcast$($message$,$ sender$\_$conn$=$None$)$: for conn in clients.keys$()$: if conn $!=$ sender$\_$conn: conn.send$($message$.$encode$())$ def send$\_$to$\_$user$($target$\_$user, message$)$: for conn, user in usernames.items$()$: if user $==$ target$\_$user: conn.send$($message$.$encode$())$ break def list$\_$files$($conn$)$: try: files $=$ os$.$listdir$($shared$\_$folder$)$ conn.send$($f$"$Files in $\{$shared$\_$folder$\}$: $\{\text{'},\text{'}.$join$($files$)\}".$encode$())$ except Exception as e: conn.send$($f$"$Error accessing files: $\{$e$\}".$encode$())$ def send$\_$file$($conn$,$ filename$)$: filepath $=$ os$.$path.join$($shared$\_$folder, filename$)$ try: with open$($filepath$,\text{'}$rb$\text{'})$ as f: conn.send$($f$"$START $\{$os$.$path.getsize$($filepath$)\}".$encode$())$ while data :$=$ f$.$read$(1024)$: conn.send$($data$)$ conn.send$("$END$".$encode$())$ except FileNotFoundError: conn.send$("$File not found.".encode$())$ def disconnect$\_$client$($conn$)$: username $=$ usernames.get$($conn$,$ "Unknown"$)$ broadcast$($f$"[\{$username$\}]$ has left", conn$)$ conn.close$()$ del clients$[$conn$]$ del usernames$[$conn$]$ def main$()$: server$\_$socket $=$ socket.socket$($socket$.$AF$\_$INET, socket.SOCK$\_$STREAM$)$ host $=$ 'localhost' port $=5555$ server$\_$socket.bind$(($host$,$ port$))$ server$\_$socket.listen$(5)$ print$($f$"$Server listening on $\{$host$\}$:$\{$port$\}")$ while True: conn, addr $=$ server$\_$socket.accept$()$ threading.Thread$($target$=$handle$\_$client, args$=($conn$,$ addr$)).$start$()$ if $\_\_$name$\_\_=="\_\_$main$\_\_"$: main$()$

client.py:

import socket

import threading

import os

import sys

def receive$\_$messages$($conn$)$:

while True:

try:

message $=$ conn.recv$(1024).$decode$()$

if message: print$($message$)$

else:

print$("$Disconnected from server."$)$

conn.close$()$

break

except Exception as e: print$($f$"$Error: $\{$e$\}")$

break

def main$($username$,$ hostname, port$)$:

conn $=$ socket.socket$($socket$.$AF$\_$INET, socket.SOCK$\_$STREAM$)$

try:

conn.connect$(($hostname$,$ port$))$

conn.send$($username$.$encode$())$

print$($conn$.$recv$(1024).$decode$())$

except Exception as e:

print$($f$"$Could not connect: $\{$e$\}")$

return

threading.Thread$($target$=$receive$\_$messages, args$=($conn$,)).$start$()$

while True: command $=$ input$($f$"\{$username$\}>")$

if command $=="/$exit$"$: conn.send$("/$exit$".$encode$())$

break elif command.startswith$("/$broadcast$")$: conn.send$($f$"/$broadcast $\{$command$\}".$encode$())$ elif command.startswith$("/$unicast$")$: conn.send$($command$.$encode$())$ elif command $=="/$files$"$: conn.send$("/$files$".$encode$())$ elif command.startswith$("/$download$")$: conn.send$($command$.$encode$())$ else: print$("$Invalid command."$)$ conn.close$()$ if $\_\_$name$\_\_=="\_\_$main$\_\_"$: if len$($sys$.$argv$)<4$: print$("$Usage: python client.py $[$username$][$hostname$][$port$]")$ else: main$($sys$.$argv$[1],$ sys$.$argv$[2],$ int$($sys$.$argv$[3]))$