def wrapper(func):
    def inner():
        print("I am the inner from the wrapper...")
    return inner

@wrapper
def caller():
    print("I am the caller...")

================

调用caller()：
I am the inner from the wrapper...

===============

问题：caller原来的print语句呢？

装饰后的caller指向了inner函数体，故调用caller()：
I am the inner from the wrapper...
而wrapper(func)的参数func指向了caller函数体，故func():
I am the caller...