I have a class A() include some method:

```
class A(self):
    def __init__ (self, x1, x2):
        self.x1 = x1
        self.x2 = x2
    def plus(self):
        X3 = self.x1 + self.x2
        return X3

```

How can I make X3 become an attribute which I can access by "self.X3" to use it for other methods
I am a newbie, thanks in advance!