code: def close_filenos(preserve):
      
      maxfd = resource.getrlimit(resource.RLIMIT_NOFILE)[1]
      if maxfd == resource.RLIM_INFINITY:
          maxfd = 4096
      for fileno in range(maxfd):
          if fileno not in preserve:
              try:
                  os.close(fileno)
              except OSError as err:
                  if not err.errno == errno.EBADF:
                      raise DaemonError(
                          'Failed to close file descriptor {0}: {1}'
                          .format(fileno, err))
docs: Close unprotected file descriptors
  
      Close all open file descriptors that are not in preserve.
  
      If ulimit -nofile is "unlimited", all is defined filenos <= 4096,
      else all is <= the output of resource.getrlimit().
  
      :param preserve: set with protected files
      :type preserve: set
  
      :return: None