import socket import threading import re #import Tkinter def ser():     s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)     s.bind(('',33333))     s.listen(1)     conn,addr=s.accept()     while True:         print '[%s:%d] send a message to me: %s'%(addr[0],addr[1],conn.recv(1024))     s.close() def clt():     c=socket.socket(socket.AF_INET,socket.SOCK_STREAM)     ip_pattern=re.compile(r'^(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])$')     while True:         ip=raw_input('Input the Server\'s IPv4 address:')         ip_match=ip_pattern.match(ip)         if ip_match:             break     c.connect((ip,33333))     while True:         sms=raw_input('Input the message you want to send:')         c.sendall(sms)     c.close() if __name__=="__main__":     ser=threading.Thread(target=ser)     clt=threading.Thread(target=clt)     ser.start()     clt.start()     ser.join()     clt.join()