code: def get_ftp(ftp_conf, debug=0):
      
      server = ftp_conf.get('server')
      user = ftp_conf.get('user')
      password = ftp_conf.get('password')
      start_path = ftp_conf.get('start_path')
      slog.info("Connecting FTP server %s ......", server)
      ftpStr = 'ftp://%s/'%server
      if start_path:
          ftpStr = ftpStr+start_path
      ftp = ftplib.FTP(server, user, password)
      ftp.set_debuglevel(debug)
      if start_path:
          ftp.cwd(start_path)
      serverFiles = ftp.nlst()
      slog.info('There are some files in %s:\n[%s]'%(ftpStr, ', '.join(serverFiles)))
      return ftp, ftpStr
docs: 得到一个 已经打开的FTP 实例，和一个 ftp 路径。
  
      :param dict ftp_conf: ftp配置文件，格式如下：
      
          >>> {
          >>>     'server':'127.0.0.1',
          >>>     'start_path':None,
          >>>     'user':'admin',
          >>>     'password':'123456',
          >>> }
  
      :returns: ftp, ftpserverstr
      :rtype: :class:`ftplib.FTP` , str