@dispatch(Node, Mapping)
def _subs(o, d):
 newargs = (subs(arg, d) for arg in o._args)
 return type(o)(*newargs)

@ dispatch ( Node , Mapping ) def _subs ( o , d ) : newargs = ( subs ( arg , d ) for arg in o . _args ) return type ( o ) ( * newargs )
returns a list of subclass strings .