Question

I want a decorator that would add the decorated function to list, like this :

class My_Class(object):

    def __init__(self):
        self.list=[]

    @decorator
    def my_function(self)
       print 'Hi'

I expect my_function to be added to self.list, but I just can’t write this decorator. If I try to write it inside My_Class, then I would have to use @self.decorator, and self does not exist since we’re outside any function. And if I try to write it out of My_Class, then I can’t retrieve self from my_function.

I know quite similar questions exist, but they are overly complicated, and I’m just learning python and decorators.

Answer 1

You can’t access self from the decorator, because the decorator is run at the time the function is defined, and at that time there are no instances of My_Class yet.

It’s better to put the function list as a class attribute instead of an instance attribute. Then you can pass this list as a parameter to the decorator:

def addToList(funcList):
    '''Decorator that adds the function to a given list'''
    def actual_decorator(f):
         funcList.append(f)
         return f
    return actual_decorator

class MyClass(object):
    funcList = []

    @addToList(funcList)
    def some_function(self, name):
        print 'Hello,', name

Now you can access MyClass.funcList to get the list of decorated functions.