code: def child(self,index):
      "helper for __getitem__/__setitem__"
      if isinstance(index,tuple):
        attr,i = index
        return getattr(self,attr)[i]
      else: return getattr(self,indexf child(self,index):
      "helper for __getitem__/__setitem__"
      if isinstance(index,tuple):
        attr,i = index
        return getattr(self,attr)[i]
      else: return getattr(self,index)
docs: helper for __getitem__/__setitem__