[masklinn]

The problem is that when you behave a certain predictable and deterministic way users will leverage that even if it's not specified.

That is actually why the Python maintainers decided to make this behaviour official: the ordering was the consequence of changes in implementation details, but over 3.6's lifecycle they feared it would cause compatibility issues as users would start relying on the ordering properties of CPython and that would be an issue for alternate implementations (though pypy had switched to the same implementation even earlier so was also insertion-ordered even when running in Python 2.7 mode).

Providing stronger guarantees was considered useful and unlikely to be severely detrimental in the long run, so the project decided to make it part of the language spec.

[thedirt0115]

"users will leverage that even if it's not specified" -- reminds me of the classic xkcd, "Workflow": https://xkcd.com/1172

[mark-r]

An xkcd in the thousands is now considered "classic"? Man I'm getting old.