code: def native_decode_source(text):
      
      if ((only_python3 and isinstance(text, bytes))
              or (only_python2 and isinstance(text, str))):
          text = decode_source_to_unicode(text)
      if only_python2:
          return text.encode('ascii', 'replace')
      return text
docs: Use codec specified in file to decode to unicode
      Then, encode unicode to native str:
          Python 2: bytes
          Python 3: unicode