code: def get_valid_filename(s, max_length=FILENAME_MAX_LENGTH):
      
      s = str(s).strip().replace(' -- @', '_')
      s = re.sub(r'(?u)[^-\w]', '_', s).strip('_')
      return s[:max_length]
docs: Returns the given string converted to a string that can be used for a clean filename.
      Removes leading and trailing spaces; converts anything that is not an alphanumeric,
      dash or underscore to underscore; converts behave examples separator ` -- @` to underscore.
      It also cuts the resulting name to `max_length`.
  
      @see https://github.com/django/django/blob/master/django/utils/text.py