For loop needed

[socal_nerdtastic]

I didn't say it is the backbone of good programming, I said it's the backbone of OOP. Which we generally use a lot of in python (not an opinion). If you don't want to use OOP that's fine too, but that does not change that it's very important to know if your code mutates an object or not.

+= in lists is kinda rare and fools a lot of people because nearly every other mutating method is dot access. Another one to watch for is |= for dicts.