code: def _get_fd(fileobj):
      
      if isinstance(fileobj, int):
          fd = fileobj
      else:
          try:
              fd = fileobj.fileno()
          except AttributeError:
              fd = None
      if fd is None or fd < 0:
          raise ValueError("invalid fileobj: {!r}".format(fileobj))
      return fd
docs: Get a descriptor out of a file object.
  
      :param fileobj:
          An integer (existing descriptor) or any object having the `fileno()`
          method.
      :raises ValueError:
          if the descriptor cannot be obtained or if the descriptor is invalid
      :returns:
          file descriptor number