code: def _safe_name(file_name, sep):
      
      file_name = stringify(file_name)
      if file_name is None:
          return
      file_name = ascii_text(file_name)
      file_name = category_replace(file_name, UNICODE_CATEGORIES)
      file_name = collapse_spaces(file_name)
      if file_name is None or not len(file_name):
          return
      return file_name.replace(WS, sep)
docs: Convert the file name to ASCII and normalize the string.