Question

I’m having some trouble with changing the value of a class at runtime and then instantiating it into an object, then storing that object inside of another class and putting that into python dictionary.

Here is a small code snippet I wrote to illustrate the problem:

import unittest

class cls1(object):

    def __init__(self, obj):
        self.obj = obj

class cls2(object):

    def __init__(self):
        self.var = 1


class Testdict(unittest.TestCase):

    def __init__(self):
        self.objs = dict()

    def runTest(self):
        obj2 = cls2()
        obj1 = cls1(cls2())

        self.objs["test1"] = obj1

        self.assertEqual(self.objs["test1"].obj.var, 1)

        cls2.var = 2
        self.assertEqual(cls2.var, 2)
        obj1 = cls1(cls2())

        self.objs["test2"] = obj1

        self.assertEqual(self.objs["test1"].obj.var, 1)
        self.assertEqual(self.objs["test2"].obj.var, 2)

if __name__ == "__main__":
    d = Testdict()
    d.runTest()

Why would cls2 not instantiate with having it’s var equal to 2?

I hope this question makes some sense.

Answer 1

What you’re showing can’t work. Ever.

class Cls2(object):
    def __init__(self):
        self.var = 1

That’s an instance variable. It’s not a class variable. You can’t access that .var with Cls2.var That variable only exists within each unique instance of the class.

        Cls2.var = 2

Does not change the self.var instance variable. That creates a new class variable in the Cls2 class.

You’d need to do something like this.

class Cls2(object):
    default= 1
    def __init__(self):
        self.var = Cls2.default

Now you can do

Cls2.default= 2

And the rest of whatever it is you’re doing should work.