code: def write_error(self, status_code: int, **kwargs: Any) -> None:
          
          if self.settings.get("serve_traceback") and "exc_info" in kwargs:
              # in debug mode, try to send a traceback
              self.set_header("Content-Type", "text/plain")
              for line in traceback.format_exception(*kwargs["exc_info"]):
                  self.write(line)
              self.finish()
          else:
              self.finish(
                  "<html><title>%(code)d: %(message)s</title>"
                  "<body>%(code)d: %(message)s</body></html>"
                  % {"code": status_code, "message": self._reason}
              )
docs: Override to implement custom error pages.
  
          ``write_error`` may call `write`, `render`, `set_header`, etc
          to produce output as usual.
  
          If this error was caused by an uncaught exception (including
          HTTPError), an ``exc_info`` triple will be available as
          ``kwargs["exc_info"]``.  Note that this exception may not be
          the "current" exception for purposes of methods like
          ``sys.exc_info()`` or ``traceback.format_exc``.