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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 get_field_callback(self, field, event):
 # type: (str, str) -> Optional[Tuple[Callable, bool]] """ Retrieves the registered method for the given event. Returns None if not found :param field: Name of the dependency field :param event: A component life cycle event :return: A 2-tuple containing the callback associated to the given event and flag indicating if the callback must be called in valid state only """

        try:
            return self.factory_context.field_callbacks[field][event]
        except KeyError:
            return None