[OJFord]

It's not breaking, it was implementation defined, now it's guaranteed order.

If a new guarantee or behaviour were a breaking change, every non-patch release of a semversioned tool (which python isn't) would be major.

[masklinn → OJFord]

> It's not breaking, it was implementation defined

And randomised at interpreter start, since Python 3.3.

[nkozyra → OJFord]

> It's not breaking

And that's sort of the problem. If it was broken, you'd know it and you'd fix/rearchitect it. Instead, it will appear to work.

[dagmx → nkozyra]

Sort of. You'd only know based on the interpreter you were using. You wouldn't know unless you tested other Python interpreters.

For example, if you wrote something in pypy it would be ordered versus cpython.