Access class static variable from super class in python

Question

I am creating a couple of 'Child' classes which are quite similar and thus wanted to group common methods in a parent class. My problem comes when trying to access static variables of the child classes from the super class.

The following code throws the error: NameError: name 'var' is not defined

class Parent:
    @staticmethod
    def do_something_with_var():
        print(var)

class Child(Parent):
    var = "Hello world"

Child.do_something_with_var()

Next thing I tried was obviously to declare var in Parent, but the same error persists.

class Parent:
    var = ""

    @staticmethod
    def do_something_with_var():
        print(var)

class Child(Parent):
    var = "Hello world"

Child.do_something_with_var()

A solution that I found was to receive the sender class, but then the call becomes a bit ugly:

class Parent:
    @staticmethod
    def do_something_with_var(cls):
        print(cls.var)

class Child(Parent):
    var = "Hello world"

Child.do_something_with_var(Child)

Anshu Kumar · Accepted Answer · 2016-04-28 10:59:47Z

3

You are confused over the usage of staticmethods(your third attempt), accessing class variables (second attempt).

What you want to do is classmethods, as shown under (Python 2.7):

class Parent(object):
    @classmethod
    def do_something_with_var(cls):
        print cls.var

class ChildA(Parent):
    var = "Child A"

ChildA.do_something_with_var()  # prints Child A

This example is equivalent to your third attempt.

answered Apr 28, 2016 at 10:59

Anshu Kumar

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1 Comment

Alejandro Daniel Noel Over a year ago

Oh, I actually tried your solution but I was still providing Child as an argument... All clear now!

zondo · Accepted Answer · 2016-04-28 10:57:10Z

1

Static scoping of the method means it is bound to the class scope as a namespace, without any reference to the class.

What you need is to have a @classmethod, so that you are able to get a reference to the class.

edited Apr 28, 2016 at 10:57

zondo

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answered Apr 28, 2016 at 10:52

Roba

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