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?

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.