Importing class variable python

Question

I have two python classes, one uses the other's variable

class A:

class A(object):

    variable = None

    @classmethod
    def init_variable(cls):
        cls.variable = something

class B:

variable = __import__('module').A.variable

class B(object):

    @staticmethod
    def method():
        return variable

I simplified my problem as much as possible. So my question is why I still have B.method() returning NoneType even if I update A.variable class variable with something using init_variable

Those are two separate variables. You may want to read about how Python variables work. — user2357112
– user2357112, Commented Aug 18, 2017 at 20:21
I think when you import module A like this you create a new instance of that module instead of importing the already existing module. Also, when do you update A.variable? — Peter
– Peter, Commented Aug 18, 2017 at 20:22
@Peter that's what I'm suspecting. In fact I'm making a package and A.variable need user input so I want B class to work with this variable when it's updated — abdelhalimresu
– abdelhalimresu, Commented Aug 18, 2017 at 20:25

Peter · Accepted Answer · 2017-08-18 20:42:33Z

1

I changed your code a bit so that it'd actually do what you want:

your_package/klass_A.py

class A(object):
    variable = None

    @classmethod
    def init_variable(cls, something):
        cls.variable = something

your_package/klass_B.py

from your_package.klass_A import A

class B(object):
    @staticmethod
    def method():
        return A.variable

Now, you can actually update A.variable and use the updated variable in B as well. For example this:

print B.method()
A.init_variable('123')
print B.method()

returns:

None
123

edited Aug 18, 2017 at 20:42

answered Aug 18, 2017 at 20:32

Peter

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