Can python functions defined inside class methods access self?

Question

Taking this class as an example:

class MyClass(object):
    def __init__(self):
        self.attribute = 4

    def my_method(self):
        def my_fun(arg1, arg2):
            self.attribute = 7

        pass

should my_fun be allowed to access and change self.attribute ?

I can see that my editor does not colour self inside my_fun.

This is what I am trying to implement: my_method should call an external function that requires a callback taking two arguments, arg1 and arg2. I would like to extend the functionality by allowing this callback to use variables declared inside my_method, and also make the my_fun callback write some debugging info to self.log. I am not quite sure if this is the right design for this type of problem.

yes, this works, you just need to actually call my_fun(val1,val2) inside my_method. try playing around with my_method and actually run it a few times — wpercy
– wpercy, Commented Feb 10, 2019 at 22:03
Yes, but simply because that function creates a closure over the self identifier, which is referencing the instance, (if called as a method on an instance) — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Feb 10, 2019 at 22:16

Primusa · Accepted Answer · 2019-02-10 22:12:03Z

7

Yes. self is just another variable. It's python automatically passing in the reference to the instance as the first argument. Nothing more.

Your inner function will be able to access self as if it were a regular function that accesses a regular object.

class MyClass(object):
    def __init__(self):
        self.attribute = 4

    def my_method(self):
        def my_fun():
            self.attribute = 7

        return my_fun

a = MyClass()
a.my_method()()
print(a.attribute)

Output:

The design you explain is fine; the one issue it has is "I would like to extend the functionality by allowing this callback to use variables declared inside my_method".

While you can access variables defined inside my_method, from a design standpoint variables that you want to save in a meaningful manner are better as attributes in the instance. You will be able to modify them and they "save" automatically, while if you want to keep the results of things you define in my_method you will have to find another place to put them when the function call ends.

edited Feb 10, 2019 at 22:12

answered Feb 10, 2019 at 22:04

Primusa

13.5k3 gold badges36 silver badges56 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

George Over a year ago

Any idea why the IDE doesn't like the self inside my_fun ?

Primusa Over a year ago

@George It's an issue with the editor not with python. It's likely an edge case that the devs haven't covered yet.

Open AI - Opting Out Over a year ago

@George report a bug to the IDE developers. Or, if it's open source, submit a patch (c:

Collectives™ on Stack Overflow

Can python functions defined inside class methods access self?

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related