code: def delete_arrays(self, period = None):
          
  
          self._memory_storage.delete(period)
          if self._disk_storage:
              self._disk_storage.delete(period)
docs: If ``period`` is ``None``, remove all known values of the variable.
  
              If ``period`` is not ``None``, only remove all values for any period included in period (e.g. if period is "2017", values for "2017-01", "2017-07", etc. would be removed)