def traverse_pre_order(start_node, get_children, filter_func=None):
 return _traverse_generic(start_node, get_parents=None, get_children=get_children, filter_func=filter_func)

def traverse_pre_order ( start_node , get_children , filter_func = None ) : return _traverse_generic ( start_node , get_parents = None , get_children = get_children , filter_func = filter_func )
generator for yielding nodes of a tree in a pre-order sort .