how to define a class variable in python 3 code example

Example: class python

class A:        # define your class A
.....

class B:         # define your class B
.....

class C(A, B):   # subclass of A and B
  
obj = C() #to create instance
# issubclass(sub, sup) boolean function returns true if the given 
# subclass sub is indeed a subclass of the superclass sup

# isinstance(obj, Class) boolean function returns true if obj is an 
# instance of class Class or is an instance of a subclass of Class