python实现简单ftp客户端的方法

#!/usr/bin/python
# -*- coding: utf-8 -*-
import ftplib
import os
import socket
HOST = 'ftp.mozilla.org'
DIRN = 'pub/mozilla.org/webtools'
FILE = 'bugzilla-3.6.9-to-3.6.10-nodocs.diff.gz'
def writedata(data):
 f = open(FILE,'wb')
 try:
 f.write(data)
 finally:
 f.close()
def main():
 try:
 f = ftplib.FTP(HOST)
 except (socket.error, socket.gaierror):
 print 'ERROR:cannot reach " %s"' % HOST
 return
 print '***Connected to host "%s"' % HOST
 try:
 f.login()
 except ftplib.error_perm:
 print 'ERROR: cannot login anonymously'
 f.quit()
 return
 print '*** Logged in as "anonymously"' 
 try:
 f.cwd(DIRN)
 except ftplib.error_perm:
 print 'ERRORL cannot CD to "%s"' % DIRN
 f.quit()
 return
 print '*** Changed to "%s" folder' % DIRN
 try:
 #传一个回调函数给retrbinary() 它在每接收一个二进制数据时都会被调用
 f.retrbinary('RETR %s' %FILE, writedata)
 except ftplib.error_perm:
 print 'ERROR: cannot read file "%s"' %FILE
 os.unlink(FILE)
 else:
 print '*** Downloaded "%s" to CWD' % FILE
 f.quit()
 return
if __name__ == '__main__':
 main()