python实现简单ftp客户端的方法

#!/usr/bin/python# -*- coding: utf-8 -*-import ftplibimport osimport socketHOST = '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()  returnif __name__ == '__main__':  main()