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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 unregister_event(self, event_name, handler):
 """ Unregister a callable that will be called when event is raised. :param event_name: The name of the event (see knack.events for in-built events) :type event_name: str :param handler: The callback that was used to register the event :type handler: function """

        try:
            self._event_handlers[event_name].remove(handler)
        except ValueError:
            pass