I am confused by this behaviour of Python(2.6.5), can someone shed light on why this happens?

Code:
class A(): 
    mylist=[]  
 
 
class B(A):
    j=0
    def addToList(self):
        self.mylist.append(1)
     

b1 = B()
print len(b1.mylist)  # prints 0 , as A.mylist is empty
b1.addToList()
print len(b1.mylist)  # prints 1 , as we have added
...