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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 event_vars(self):
 """The service's eventable variables. Returns: list(tuple):
 A list of (variable name, data type) tuples. """

        if self._event_vars is None:
            self._event_vars = list(self.iter_event_vars())
        return self._event_vars