如何使用实例方法作为装饰器？

Question

How the following code works, without passing the function (func) to the object method task().

class Pipeline:
    def __init__(self):
        self.tasks = list()
        
    def task(self):
        def inner(func):
            self.tasks.append(func)
            return func
        return inner

pipeline = Pipeline()
    
@pipeline.task()
def first_task(x):
    return x + 1

print(pipeline.tasks)

For example, comparing it to the following. Adding additional functionality to a given function. I just can't figure out in the above example how the func is getting passed to task() method.

def logger(func):
    def inner(*args):
        print('Calling function: {}'.format(func.__name__))
        print('With args: {}'.format(args))
        return func(*args)
    return inner

@logger
def add(a, b):
    return a + b

Answer 1

Here:

@pipeline.task()
def first_task(x):
    return x + 1

pipeline.task() calls the task method of pipeline . This returns the function inner .

The @ indicates that this function ( inner ) is to be used as a decorator. So inner is called and the subsequent function definition def first_task... is passed as its argument, func .

inner adds the function func to the pipeline's list of tasks.

You can read it as something like:

inner = pipeline.task()
# inner is a function created by pipeline.task()
#  to add a function to the pipeline's task list
@inner
def first_task(x):
    return x + 1

And decorator syntax makes this behave similarly to:

inner = pipeline.task()
def first_task(x):
    return x + 1
first_task = inner(first_task)