code: def decode_argument(self, value: bytes, name: str = None) -> str:
          
          try:
              return _unicode(value)
          except UnicodeDecodeError:
              raise HTTPError(
                  400, "Invalid unicode in %s: %r" % (name or "url", value[:40])
              )
docs: Decodes an argument from the request.
  
          The argument has been percent-decoded and is now a byte string.
          By default, this method decodes the argument as utf-8 and returns
          a unicode string, but this may be overridden in subclasses.
  
          This method is used as a filter for both `get_argument()` and for
          values extracted from the url and passed to `get()`/`post()`/etc.
  
          The name of the argument is provided if known, but may be None
          (e.g. for unnamed groups in the url regex).