How to implement “__iadd__()” for an immutable type?

Question

I would like to subclass an immutable type or implement one of my own which behaves like an int does as shown in the following console session:

Answer 1

The return value of __iadd__() is used. You don't need to return the object that's being added to; you can create a new one and return that instead. In fact, if the object is immutable, you have to.

import os.path

class Path(str):
    def __iadd__(self, other):
        return Path(os.path.join(str(self), str(other)))

path = Path("C:\\")
path += "windows"

print path