setting a class attribute using a class method in python

Question

I have a class with a few class attributes, that I would like to initialize by using class methods. This is because I have close to 300 items in a list, and I'd rather not have them in the class definition. Since I will be having at minimum, upwards of a few hundred objects of this class, It wouldn't be efficient to read and then create a attribute for each individual instantiation when they won't be modifiying the two lists I've defined, and only reading from them.

class exampleClass:

    @classmethod
    def getUnsupportedEvents(cls):
        with open("randomfile.json") as file:
            return json.load(file)

    supportedEvents = []
    unsupportedEvents = getUnsupportedEvents()

I want to set the class attribute unsupportedEvent using the classmethod getUnsupportedEvents(), but when I attempt to do so in the above way, I get the following error:

unsupportedEvents = getUnsupportedEvents()

TypeError: 'classmethod' object is not callable

This seems really simple, am I just overlooking something really easy?

This code should give a NameError for getUnsupportedEvents — Mustafa Aydın
– Mustafa Aydın, Commented May 7, 2020 at 9:38
If you want to assign inside the class just drop parenthesis unsupportedEvents = getUnsuportedEvents — dhentris
– dhentris, Commented May 7, 2020 at 9:41
@dhentris that would bind the function to the variable, which isn't what I want. I want it to execute and return the value of the function to be stored as a class attribute — user5423
– user5423, Commented May 7, 2020 at 10:11

Serge Ballesta · Accepted Answer · 2020-05-07 09:38:25Z

1

You are trying to use a class method before the class is fully defined. You must delay the call after the definition:

class exampleClass:

    @classmethod
    def getUnsupportedEvents(cls):
        with open("randomfile.json") as file:
            return json.load(file)

    supportedEvents = []

exampleClass.unsupportedEvents = exampleClass.getUnsuportedEvents()

answered May 7, 2020 at 9:38

Serge Ballesta

150k13 gold badges137 silver badges267 bronze badges

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

4 Comments

user5423 Over a year ago

If I was to import this class into my main program, would issues not arise as that line of code is outside the class?

Serge Ballesta Over a year ago

You load modules and import symbols. In order to import the class, the module will be loaded and the line of code will be executed. Of course it has to be in the same module as the class definition after that definition.

user5423 Over a year ago

Would the entire module be loaded even if I were to import specific classes from the module, i.e. ``` from exampleModule import exampleClass``` where exampleModule has several classes.

Serge Ballesta Over a year ago

Exactly. That is the reason why I said you load (full) modules and import (some) symbols. In fact from mod import symb first loads the full mod module and then import sym in the local (or module global) symbol table.

Collectives™ on Stack Overflow

setting a class attribute using a class method in python

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related