python使用socket非阻塞编程

import socket, sys
lstn = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
lstn.bind(('', 2000))
lstn.listen(5)

v = ''
cs = []
nc = 2

for i in range(nc):
    (clnt,ap) = lstn.accept()
    clnt.setblocking(0)
    cs.append(clnt)
    
while (len(cs) > 0):
    clnt = cs.pop(0)
    cs.append(clnt)
    try:
        k = clnt.recv(1)
        
        if k == '':
            clnt.close()
            cs.remove(clnt)
            
        v += k
        clnt.send(v)
    except: pass

lstn.close()
print 'the final value of v is', v
=============================================================

import socket, sys
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('127.0.0.1', 2000))

while(1):
     k = raw_input('enter a letter:')
     s.send(k)
     if k == '': break
     v = s.recv(1024)
     print v

s.close()