1. operators use special lookup for dunder methods--on class, not on instance: >>> a+1 # lookup on class 1+1 2 >>> a.__add__(1) # instance me

1. operators use special lookup for dunder methods--on class, not on instance: >>> a+1 # lookup on class 1+1 2 >>> a.__add__(1) # instance method 0 2. There is __radd__ that is called if __add__ doesn't support given types (for different types).