Question

I know about the __add__ method to override plus, but when I use that to override +=, I end up with one of two problems:

1. if __add__ mutates self, then

   z = x + y 

   will mutate x when I don’t really want x to be mutated there.

2. if __add__ returns a new object, then

   tmp = z z += x z += y tmp += w return z 

   will return something without w since z and tmp point to different objects after z += x is executed.

I can make some sort of .append() method, but I’d prefer to overload += if it is possible.

Answer 1

Yes. Just override the object’s __iadd__ method, which takes the same parameters as add. You can find more information here.