code: def positions(self):
          
          # if accessing and stale - update first
          if self.root.stale:
              self.root.update(self.root.now, None)
  
          vals = pd.DataFrame({x.name: x.positions for x in self.members
                               if isinstance(x, SecurityBase)})
          self._positions = vals
          return vals
docs: TimeSeries of positions.