def add_handler(self, handler):
        """Add a handler object.

        :Parameters:
            - `handler`: the object providing event handler methods
        :Types:
            - `handler`: `EventHandler`
        """
        if not isinstance(handler, EventHandler):
            raise TypeError("Not an EventHandler")
        with self.lock:
            if self.handlers in handler:
                return
            self.handlers.append(handler)
            self._update_handlers()
dataset/ETHPy150Open kuri65536/python-for-android/python3-alpha/python-libs/pyxmpp2/mainloop/events.py/EventDispatcher.add_handler/swapped operands of `in`