python - How would I access variables from one class to another?

Question

I am writing a program that is utilizing multiple classes. I have one class that is dedicated to determining values for a set of variables. I would then like to be able to access the values of those variables with other classes. My code looks as follows:

class ClassA(object):
    def __init__(self):
        self.var1 = 1
        self.var2 = 2

    def methodA(self):
        self.var1 = self.var1 + self.var2
        return self.var1


class ClassB(ClassA):
    def __init__(self):
        self.var1 = ?
        self.var2 = ?

object1 = ClassA()
sum = object1.methodA()
print sum

I use classA to initialize 2 variables (var1 and var2). I then use methodA to add them, saving the result as var1 (I think this will make var1 = 3 and var2 = 2). What I want to know is how would I have ClassB then be able to get the values for var1 and var2 from ClassA?

question from:https://stackoverflow.com/questions/19993795/how-would-i-access-variables-from-one-class-to-another

Answer 1

var1 and var2 are instance variables. That means that you have to send the instance of ClassA to ClassB in order for ClassB to access it, i.e:

class ClassA(object):
    def __init__(self):
        self.var1 = 1
        self.var2 = 2

    def methodA(self):
        self.var1 = self.var1 + self.var2
        return self.var1



class ClassB(ClassA):
    def __init__(self, class_a):
        self.var1 = class_a.var1
        self.var2 = class_a.var2

object1 = ClassA()
sum = object1.methodA()
object2 = ClassB(object1)
print sum

On the other hand - if you were to use class variables, you could access var1 and var2 without sending object1 as a parameter to ClassB.

class ClassA(object):
    var1 = 0
    var2 = 0
    def __init__(self):
        ClassA.var1 = 1
        ClassA.var2 = 2

    def methodA(self):
        ClassA.var1 = ClassA.var1 + ClassA.var2
        return ClassA.var1



class ClassB(ClassA):
    def __init__(self):
        print ClassA.var1
        print ClassA.var2

object1 = ClassA()
sum = object1.methodA()
object2 = ClassB()
print sum

Note, however, that class variables are shared among all instances of its class.