code: def locale(self) -> tornado.locale.Locale:
          
          if not hasattr(self, "_locale"):
              loc = self.get_user_locale()
              if loc is not None:
                  self._locale = loc
              else:
                  self._locale = self.get_browser_locale()
                  assert self._locale
          return self._locale
docs: The locale for the current session.
  
          Determined by either `get_user_locale`, which you can override to
          set the locale based on, e.g., a user preference stored in a
          database, or `get_browser_locale`, which uses the ``Accept-Language``
          header.
  
          .. versionchanged: 4.1
             Added a property setter.