code: def AddEventSource(self, event_source):
      
      self._RaiseIfNotWritable()
  
      self._storage_file.AddEventSource(event_source)
      self.number_of_event_sources += 1
docs: Adds an event source.
  
      Args:
        event_source (EventSource): an event source.
  
      Raises:
        IOError: when the storage writer is closed.
        OSError: when the storage writer is closed.