socket编程的好例子！
echo sever 与　echo client。
echo server 接受连接并把收到的数据原样发回。
echo client  发起连接到服务器，发送数据包并且接受对方返回的数据。

echo server:

import socket

HOST = '127.0.0.1'
PORT = 10007
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((HOST, PORT))
s.listen(1)
conn, addr = s.accept()
print 'Connected by', addr
while 1:
    data = conn.recv(1024)
    if not data: break
    conn.send(data)
conn.close()

echo client:

import socket

HOST = '127.0.0.1'
PORT = 10007
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
s.send('Hello, world')
data = s.recv(1024)
s.close()
print 'Received', repr(data)