<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def attach(self, engine, log_handler, event_name):
 """Attach the logger to the engine and execute `log_handler` function at `event_name` events. Args: engine (Engine):
 engine object. log_handler (callable):
 a logging handler to execute event_name: event to attach the logging handler to. Valid events are from :class:`~ignite.engine.Events` or any `event_name` added by :meth:`~ignite.engine.Engine.register_events`. """

        if event_name not in State.event_to_attr:
            raise RuntimeError("Unknown event name '{}'".format(event_name))

        engine.add_event_handler(event_name, log_handler, self, event_name)