为什么类实例装饰器会跳过代码？

Question

Try running the code below. Why does the output only print the "gets skipped" one time? We call rotate_list three times and I don't understand why it doesn't run all of the code inside __call__() each time. My guess is that it is only printing it once for instantiation or something.

class anothercall:
    def __init__(self):
        self.enabled = True
    def __call__(self,f):
        print("gets skipped")
        
        def wrap(*args, **kwargs):
            if self.enabled:
                print('calling {}'.format(f))
            return f(*args, **kwargs)
        return wrap

another = anothercall()
@another
def rotate_list(l):
    return l[1:] + [l[0]]
    
l = [1,2,3]
rotate_list(l)
l = [1,2,3]
rotate_list(l)
l = [1,2,3]
rotate_list(l)

Answer 1

another is called when you define rotate_list , not when you call rotate_list . The name rotate_list is rebound to whatever another returns.

@another
def rotate_list(l):
    ...

is equivalent to

def rotate_list(l):
    ...

rotate_list = another(rotate_list)

Answer 2

When python interpreter encounters a function with a decorator it changes the function with the wrapper function. For your program rotate_list = another(rotate_list) happen in line 14. This calling the __call__ method so it's printing "gets skipped" once.

Then when you call rotate_list function it is just calling wrap function.