code: def add_event(self, key, event):
          
          if self.key_exists(key):
              # This check might actually also be done further up in the chain
              # (read: SQLiteEventStore). Could potentially be removed if it
              # requires a lot of processor cycles.
              msg = "The key already existed: {0}".format(key)
              raise EventStore.EventKeyAlreadyExistError(msg)
  
          self._rotate_files_if_needed()
  
          # Since I guess LogEventStore is less mature codewise than
          # SQLiteEventStore I am writing to that log file first. If something
          # fails we are not writing to SQLiteEventStore.
          for store in self.stores:
              store.add_event(key, event)
          self.count += 1
docs: Add an event and its corresponding key to the store.