code: def is_byte_range_valid(start, stop, length):
      
      if (start is None) != (stop is None):
          return False
      elif start is None:
          return length is None or length >= 0
      elif length is None:
          return 0 <= start < stop
      elif start >= stop:
          return False
      return 0 <= start < length
docs: Checks if a given byte content range is valid for the given length.
  
      .. versionadded:: 0.7