Python: function attributes inside a class

Question

class Vec:

def __init__ (self,x,y):
self.x=x
print(self.x)
print("=====x=====")
self.y=y
print(self.y)
print("=====y=====")

def __add__ (self,other):
print(other.x) ### how did we get to the value 1 here?
print("=====xxx=====")
print(other.y). ### how did we get to the value 2 here?
print("=====yyy=====")
return Vec(self.x+other.x,self.y+other.y) <-- ***

v1=Vec(3,4)
v2=Vec(1,2)
r=v1+v2

print(r.x+r.y) ###outputs 10

*** I don't really understand why other.x and other.y has v2's values (while self.x and self.y has v1's values).

Answer 1

v1 + v2 invokes the v1.__add__(v2) magic method. So v1 is the "self" part and v2 is the "other" part.

If it were the other way...

v2 + v1 would invoke v2.__add__(v1).