result.py

class GetResult:

    def __init__(self):
        self.result=[] #here i have changed
    def add(self,x,y):
        z= x+y
        self.result.append(z)
rs=GetResult()
rs.add(1,2) #the result is [3]
print rs.result
rs.add(3,4)#the result is [3, 7] #what i want the is [7] !!!!!!
print rs.result