装饰器在没有被调用的情况下运行

Question

我已经深入研究了 Python 装饰器，并且正在尝试一些向装饰器添加函数参数的方法。

我面临的问题与我想在装饰器中进行递归有关，同时仅在初始调用时设置一些变量。因此，在示例中，我只想在函数调用中打印一次消息。

现在它打印在函数定义上，而不是函数调用上。请参阅此示例代码：

def recursiveCounter(message):
    def decorater(func):
        def wrapper(count):
            func(count)
            if count < 10:
                count += 1
                wrapper(count)

        print message
        return wrapper
    return decorater


@recursiveCounter("hello I was called once")
def counter(count):
    print count


counter(0)

Answer 1

下面我添加了 cmets 来指示每行运行的时间：

def recursiveCounter(message):  # when the decorator is defined
    def decorater(func):  # when the decorator is created - @recursiveCounter("hello I was called once")
        def wrapper(count):  # when the function is decorated - def counter(count): print count
            func(count)  # when the function is called - counter(0)
            if count < 10:  # when the function is called
                count += 1  # when the function is called 
                wrapper(count)  # when the function is called

        print message  # **when the function is decorated**
        return wrapper  # when the function is decorated
    return decorater  # when the decorator is created

如您所见，print message 行在函数被修饰时运行，而不是在它被调用时运行。如果你想让它在函数被调用时运行，你应该将它缩进一层，所以它在wrapper而不是decorater内。

---

如果您真的想保留递归实现，请重新排列包装器以定义并调用递归本身：

...
def wrapper(count):
    def inner_wrapper(count):
        if count < 10:
            inner_wrapper(count + 1)
    inner_wrapper(count)
    print message