def _filter_nodes(superclass, all_nodes=_all_nodes):
 node_names = (node.__name__ for node in all_nodes if issubclass(node, superclass))
 return frozenset(node_names)

def _filter_nodes ( superclass , all_nodes = _all_nodes ) : node_names = ( node . __name__ for node in all_nodes if issubclass ( node , superclass ) ) return frozenset ( node_names )
filter out ast nodes that are subclasses of superclass .