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