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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 add_breakpoint(self, event_type, bp):
 """ Adds a breakpoint which would trigger on `event_type`. :param event_type: The event type to trigger on :param bp: The breakpoint :return: The created breakpoint. """

        if event_type not in event_types:
            raise ValueError("Invalid event type %s passed in. Should be one of: %s" % (event_type,
                                                                                        ", ".join(event_types))
                             )
        self._breakpoints[event_type].append(bp)