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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def attach_event_handler(canvas, handler=close_on_esc_or_middlemouse):
 """ Attach a handler function to the ProcessedEvent slot, defaulting to closing when middle mouse is clicked or escape is pressed Note that escape only works if the pad has focus, which in ROOT-land means the mouse has to be over the canvas area. """

    if getattr(canvas, "_py_event_dispatcher_attached", None):
        return

    event_dispatcher = C.TPyDispatcherProcessedEvent(handler)
    canvas.Connect("ProcessedEvent(int,int,int,TObject*)",
                   "TPyDispatcherProcessedEvent", event_dispatcher,
                   "Dispatch(int,int,int,TObject*)")

    # Attach a handler only once to each canvas, and keep the dispatcher alive
    canvas._py_event_dispatcher_attached = event_dispatcher