Question

我有以下代码，它可以工作并给出正确的输出：

def msg_before(msg=None):
    def actual_decorator(func):
        def wrapper(*args, **kwargs):
            print(msg if msg is not None else "was none")  # original
            result = func(*args, **kwargs)
            return result
        return wrapper
    return actual_decorator


@msg_before("this comes before")
def test_func():
    print("test")


if __name__ == "__main__":
    test_func()

输出：

this comes before
test

但是当我像这样更改wrapper函数时：

def msg_before(msg=None):
    def actual_decorator(func):
        def wrapper(*args, **kwargs):
            msg = msg if msg is not None else "was none"  # changed
            print(msg)                                    # changed
            result = func(*args, **kwargs)
            return result
        return wrapper
    return actual_decorator

我收到以下错误：

Traceback (most recent call last):
  File "C:/Users/ruohola/Desktop/test.py", line 33, in <module>
    test_func()
  File "C:/Users/ruohola/Desktop/test.py", line 19, in wrapper
    msg = msg if msg is not None else "was none"  # changed
UnboundLocalError: local variable 'msg' referenced before assignment

在我看来，这两个代码是完全相同的，我只是不了解错误的出处以及为什么在第一个代码中没有发生该错误？

访问嵌套函数中的外部函数参数会产生奇怪的行为？

0 个答案: