The curious case of the else in Python loops

One of the first things to stand out when I was starting with Python was the else clause. I guess everyone knows the normal usage of such clauses in any programming language, which is to define an alternate path for the if condition. Oddly enough, in Python we can add else clauses in loop constructions, such as for and while.

For example, this is valid Python:

for number in some_sequence:
    if is_the_magic_number(number):
        print('found the magic number')
        break
else:
    print('magic number not found')

Notice how the else is aligned with the for and not with the if. What this means is that commands inside the else block will be executed if, and only if, the loop was not finished by a break. The same is true for while loops.

I must admit that I’ve always had some trouble to remember the meaning of an else in loops, specially because I don’t see them very often (and I’m grateful for that). But, at some day I was watching Raymond Hettinger’s Transforming Code into Beautiful, Idiomatic Python talk where he brilliantly says something like this at some point:

Why don’t you call the else in loops as ‘nobreak’?

That’s all I needed to not forget the meaning anymore. 🙂