How to access a class variable from another class in python?

Question

I have the following code segment :

class A:
    def __init__(self):
        self.state = 'CHAT'

    def method1(self):
        self.state = 'SEND'

    def printer(self):
        print self.state


class B(A):
    def method2(self):
        self.method1()
        print self.state

ob_B = B()
ob_A = A()
ob_B.method2()
ob_A.printer()

This gives me the output :

SEND
CHAT

I want it to print :

SEND
SEND

That is, when B.method2 is modifying self.state by calling self.method1, I want it to modify the already existing value of self.state = 'CHAT' in A's instance. How can I do this?

You have instance attributes, and those are specific to the instances. You are not actually calling ob_B.method2. — Martijn Pieters
– Martijn Pieters, Commented Apr 26, 2013 at 10:21
That is my problem. I want self.state to be a class variable, and then have it initialized when an object of A is created. — Indradhanush Gupta
– Indradhanush Gupta, Commented Apr 26, 2013 at 10:24

jamylak · Accepted Answer · 2013-04-26 10:25:00Z

5

The instance is passed as the first argument to each of your methods, so self is the instance. You are setting instance attributes and not class variables.

class A:

    def __init__(self):
        A.state = 'CHAT'

    def method1(self):
        A.state = 'SEND'

    def printer(self):
        print A.state


class B(A):
    def method2(self):
        self.method1()
        print B.state

ob_B = B()
ob_A = A()
ob_B.method2()
ob_A.printer()

SEND
SEND

answered Apr 26, 2013 at 10:25

jamylak

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2 Comments

Indradhanush Gupta Over a year ago

Thanks. This does it nicely. :) But just being inquisitive, say self.state is an instance variable. Is their a way to access it from class B?

jamylak Over a year ago

@IndradhanushGupta Yes, it's part of the instance so it doesn't matter which class you are in unless you have overridden it in B, you just access it like self.x,

James · Accepted Answer · 2013-04-26 10:25:07Z

0

ob_B = B()
ob_A = A()
ob_B.method2()
ob_A.printer()

You need to call ob_B.method2() -- without the parentheses that statement is just a reference to the function and doesn't actually call it.

answered Apr 26, 2013 at 10:25

James

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2 Comments

aldeb Over a year ago

That doesn't change anything to the current problem.

jamylak Over a year ago

Don't worry that was just a typo, his output matches up when you fix this

Ansuman Bebarta · Accepted Answer · 2013-04-26 10:28:32Z

0

You can call the printer() method by using object of B so that you will get the updated value.

ob_B = B()
ob_A = A()
ob_B.method2()
ob_B.printer()

answered Apr 26, 2013 at 10:28

Ansuman Bebarta

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