[Python知识库]python装饰器recursive_repr执行理解

recursive_repr(fillvalue=’,’)

python装饰器的使用
其中recursive_repr装饰器的目的是防止递归，提供指定返回值fillvalue
在实例化Mylist为对象m后，再递归调用m.append(m)，执行两次wrapper。原因是第一次执行wrapper后进入def __repr__后，有一个递归对象m，再执行wrapper。

from _thread import get_ident


def recursive_repr(fillvalue=',,,'):
    'Decorator to make a repr function return fillvalue for a recursive call'

    def decorating_function(user_function):
        repr_running = set()

        def wrapper(self):
            key = id(self), get_ident()
            print("key",key)
            print("repr_running_1",repr_running)
            if key in repr_running:
                return fillvalue
            repr_running.add(key)
            try:
                print("1111111111")
                result = user_function(self)
                print("-------")
            finally:
                repr_running.discard(key)
            print("repr_running_2",repr_running)
            print('//n')
            return result

        # Can't use functools.wraps() here because of bootstrap issues
        wrapper.__module__ = getattr(user_function, '__module__')
        wrapper.__doc__ = getattr(user_function, '__doc__')
        wrapper.__name__ = getattr(user_function, '__name__')
        wrapper.__qualname__ = getattr(user_function, '__qualname__')
        wrapper.__annotations__ = getattr(user_function, '__annotations__', {})
        return wrapper

    return decorating_function

class MyList(list):
     @recursive_repr()
     def __repr__(self):
         return '<' + '|'.join(map(repr,self)) + '>'



m = MyList('sdsd')
print(m)
m.append('x')
print(m)
m.append(m) /*执行两次wrapper*/
print(m)