Best way to access class member in a class in Python

Question

I want to know which one is the best way to access the class variable in a class, either by self, or by class name

I have read somewhere that self is only used for accessing the instance variable. But when I tried with the below code, it is one of the same things. Is is it mean that we can use either of them?

class MyClass:
    cls_var = 0 # class variable

    def increment(self, incre):
        self.cls_var += incre
        MyClass.cls_var += incre

    def print_var(self):
        print(self.cls_var) #Choice 1
        print(MyClass.cls_var) # Choice 2


obj1 = MyClass()
obj2 = MyClass()

obj1.increment(5)
obj2.increment(10)

obj1.print_var() #prints 5, 15
obj2.print_var() # prints 15, 15

Depends on what you want, a class variable can be inherited (and overwritten). So in that sense it is better to access it through self if you want to be able to alter it in a child class. — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Jan 27, 2018 at 13:13
It prints 5, 15, 15, 15. can someone explain how we get this result please? — kmario23
– kmario23, Commented Jan 27, 2018 at 14:57

Arnav Borborah · Accepted Answer · 2018-01-27 13:40:49Z

1

You should access a class variable only by class name, since that variable is shared among all classes. Thus, to avoid confusion, one should only access class variables by the name of the class; otherwise it might lead to surprising errors (See the second snippet).

answered Jan 27, 2018 at 13:40

Arnav Borborah

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Comments

J. Katzer · Accepted Answer · 2018-01-27 13:31:25Z

0

In my opinion you should use "Choice 2", as the class variable "cls_var" is shared by all instances. So if you do

ob1.increment(5)

also "ob2.cls_var" gets incremented, but Zen of Python sais that explicit is better than implicit! So do

MyClass.increment(5)

See: https://docs.python.org/2/tutorial/classes.html#class-and-instance-variables.

answered Jan 27, 2018 at 13:31

J. Katzer

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