(node,walker)
return None
Depth-first descent into the node hierarchy.
    
    See docstring for hier.Walker for information on the given visitor.
Depth-first descent into the node hierarchy.
    
    See docstring for hier.Walker for information on the given visitor.
Depth - first descent into the node hierarchy . See docstring for hier . Walker for information on the given visitor .
def walk(node,walker):
    '''
    Depth-first descent into the node hierarchy.
    
    See docstring for hier.Walker for information on the given visitor. 
    '''
    value,bail = walker(node)
    if value is not None or bail: return value

    for sn in node.nodes:
        value = bail = walk(sn,walker)
        if value is not None: return value
        continue
    return None
def walk ( node , walker ) : value , bail = walker ( node ) if value is not None or bail : return value for sn in node . nodes : value = bail = walk ( sn , walker ) if value is not None : return value continue return None