Working around decorator and getattr

Question

I have problem solving this question, I have the following class:

class test:

    @auth
    def method1(self, x):
        return x

    @auth
    def method2(self, x, y):
        return x+y

    def method3(self, z):
        return z

I applied the decorator in both methods, follow:

class auth:

    def __init__(self, f):
        self.f = f

    def __call__(self, *args, **kwargs):
        self.f(*args, **kwargs)

So far no problem, however I need (NEED) to use the following code:

def run():
    klass = globals()["test"]()

    method1 = getattr(klass, "method1")
    print(method1.__code__.co_varnames)
    # should print (self, x)

    method2 = getattr(klass, "method2")
    print(method2.__code__.co_varnames)
    # should print (self, x, y)

    method3 = getattr(klass, "method3")
    print(method3.__code__.co_varnames)
    # i get (self, z) < without decorator

But I get now:

 AttributeError: 'auth' object has no attribute '__code__'

What makes sense if we think that the signature of method "method1 and method2" is now "auth".

So how do I get the arguments with or without decorators. I started reading about the "inspect" but there are many reports about being slow.

You could use something like `method1.f.__code__.co_varnames`. But in general the code that you "need" to use is going to need to be aware of/cooperative with the decorator code (i.e., it needs to know where to look to find the function arguments). — BrenBarn, Jun 12 '17 at 19:03

score 1 · Accepted Answer · answered Jun 12 '17 at 19:00

1

The "original" method is stored in the f attribute of the auth object. Instead of method1.__code__.co_varnames use method1.f.__code__.co_varnames

answered Jun 12 '17 at 19:00

Patrick Haugh

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love you bro! it's possible to know if a method has decorator or not ? (just a small question) – Jonny Jun 12 '17 at 19:01
I'm not sure, but [this](https://stackoverflow.com/questions/19314405/how-to-detect-is-decorator-has-been-applied-to-method-or-function) might be somewhere to start – Patrick Haugh Jun 12 '17 at 19:04
thanks, i can use __code__ != None instead inspect.getargspec like the link, but anyway thanks man. – Jonny Jun 12 '17 at 19:06

cmdLP · Answer 2 · 2017-06-12T19:16:25.223

Annotations just contain an object and are not the object itsself, it is an object of class auth and not function. To access the function itsself, you can write methodN.f.__code__.co_varnames or assign a copy of the __dict__ object of the function to the auth-object in __init__ itsself.

class auth:

    def __init__(self, f):
        self.__dict__.update(f.__dict__)
        # now the initialisations
        self.f = f

    def __call__(self, *args, **kwargs):
        self.f(*args, **kwargs)

Edit: You should initialize the members/call super after updating the dict, because f could be overriden by the update, eg. you define another decorator-class and it has also a member f.

Thanks, it's solved and great workaround with dict update – Jonny Jun 12 '17 at 19:07 — Jonny, Jun 12 '17 at 19:07

Working around decorator and getattr

2 Answers2