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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 ProduceEventSource(self, event_source):
 """Produces an event source. Args: event_source (EventSource):
 an event source. Raises: RuntimeError: when storage writer is not set. """

    if not self._storage_writer:
      raise RuntimeError('Storage writer not set.')

    self._storage_writer.AddEventSource(event_source)
    self._number_of_event_sources += 1

    self.last_activity_timestamp = time.time()