Can someone provides a detail explanation why this is happening? How does Python compiler create class variables in this case?
class A(object): x = 1 y = x + 1 class B(A): x = 10 >>> B.x 10 >>> B.y 2 # ---> I was expecting 11 here, why does this y still uses the A's value? Because class variables are evaluated at the same time the class itself is evaluated. Here the sequence of events is: A is defined and the values in it are set, so x is 1 and y is 2. Then B is defined, and the x entry in B is set to 10. Then you access B.y, and since there is no y entry in B, it checks its parent class. It does find a y entry in A, with a value of 2. y is defined only once.
If you really want such a variable, you may want to define a class method.
class A: x = 1 @classmethod def y(cls): return cls.x + 1 class B(A): x = 10 >>> B.y() 11 
inheritance.
A and B inherit from object.B did not inherit from A, but based on the context of the question it was clearly meant to.This is because y is a class attribute that belongs to A, so changing the value of x in a class instance of B does not change the value of y. You can read more about that in the documentation: https://docs.python.org/2/tutorial/classes.html#class-objects
y is fixed using the value of x at the time it is defined.It does not do that.
>>> class A(object): ... x = 1 ... y = x + 1 ... >>> class B(object): ... x = 10 ... >>> B.x 10 >>> B.y Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: type object 'B' has no attribute 'y' 
class B(A).A and B do not share variables even though they both inherit from the same parent class.