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()