還是那個題目（題目和流程見java版本），感覺光用java寫一點新意也沒有，恰巧剛學習了python，何不拿來一用，呵呵：
服務器端：

import SocketServer, time  class MyServer(SocketServer.BaseRequestHandler):    userInfo = {      'yangsq'  : 'yangsq',      'hudeyong' : 'hudeyong',      'mudan'   : 'mudan' }     def handle(self):      print 'Connected from', self.client_address            while True:        receivedData = self.request.recv(8192)        if not receivedData:          continue               elif receivedData == 'Hi, server':          self.request.sendall('hi, client')                  elif receivedData.startswith('name'):          self.clientName = receivedData.split(':')[-1]          if MyServer.userInfo.has_key(self.clientName):            self.request.sendall('valid')          else:            self.request.sendall('invalid')                    elif receivedData.startswith('pwd'):          self.clientPwd = receivedData.split(':')[-1]          if self.clientPwd == MyServer.userInfo[self.clientName]:            self.request.sendall('valid')            time.sleep(5)             sfile = open('PyNet.pdf', 'rb')            while True:              data = sfile.read(1024)              if not data:                break             while len(data) > 0:                intSent = self.request.send(data)                data = data[intSent:]             time.sleep(3)            self.request.sendall('EOF')          else:            self.request.sendall('invalid')                    elif receivedData == 'bye':          break      self.request.close()            print 'Disconnected from', self.client_address      print  if __name__ == '__main__':    print 'Server is started/nwaiting for connection.../n'    srv = SocketServer.ThreadingTCPServer(('localhost', 50000), MyServer)    srv.serve_forever()       

說明：
line-55到line-58的作用就相當于java中某個類里面的main函數，即一個類的入口。
python中SocketServer module里提供了好多實用的現成的類，BaseRequestHandler就是一個，它的作用是為每一個請求fork一個線程，只要繼承它，就有這個能力了，哈哈，真是美事。
當然，我們繼承了BaseRequestHandler，就是override它的handle方法，就像java中繼承了Thread后要實現run方法一樣。實際上這個handle方法的內容和我們的java版本的run函數實現的完全一樣。
line-30到line-43就是處理文件下載的主要內容了。看著都挺眼熟的呵：）
這里在文件發送完后發了一個“EOF”，告訴client文件傳完了。
客戶端：

import socket, time  class MyClient:     def __init__(self):      print 'Prepare for connecting...'     def connect(self):      sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)      sock.connect(('localhost', 50000))       sock.sendall('Hi, server')      self.response = sock.recv(8192)      print 'Server:', self.response       self.s = raw_input("Server: Do you want get the 'thinking in python' file?(y/n):")      if self.s == 'y':        while True:          self.name = raw_input('Server: input our name:')          sock.sendall('name:' + self.name.strip())          self.response = sock.recv(8192)          if self.response == 'valid':            break         else:            print 'Server: Invalid username'         while True:          self.pwd = raw_input('Server: input our password:')          sock.sendall('pwd:' + self.pwd.strip())          self.response = sock.recv(8192)          if self.response == 'valid':            print 'please wait...'             f = open('b.pdf', 'wb')            while True:              data = sock.recv(1024)              if data == 'EOF':                break             f.write(data)                          f.flush()            f.close()             print 'download finished'            break         else:            print 'Server: Invalid password'                 sock.sendall('bye')      sock.close()      print 'Disconnected'   if __name__ == '__main__':    client = MyClient()    client.connect()