The title of the post is misleading: it means "ordered by insertion order" (not sorted).

Previously it was unpredictable, and that's why collections have OrderedDict; which makes sense instead of trusting an implementation detail of CPython from 3.6.

Is not mentioned in the docs: https://docs.python.org/3/library/stdtypes.html#mapping-type...

EDIT: but the behaviour is documented in OrderedDict itself! https://docs.python.org/3/library/collections.html?highlight...

Interesting!

I wonder why OrderedDict isn't outright deprecated (or reimplemented as a trivial wrapper over dict).

You can get the first/last key of a 3.8 dict with dict.keys() and reversed(dict.keys()) which you can then delete to reimplement OrderedDict.popitem.

Deleting a key and reinserting it will let you reimplement move_to_end.

The only cool thing that OrderedDict's implementation might be useful for is to move to front (or anywhere else not the back) but it doesn't expose that api.

When OrderedDict is compared with another OrderedDict, it also checks whether the order of items is the same (this way also violating LSP, but that's another story), dict instances don't do that.

Thanks, I just learned something.

...thats the same thing. Maybe youre thinking about "sorted maps"?

It's not the same thing. Compare two OrderedDicts that weren't constructed in the same order and the comparison will fail. Compare two dicts that weren't constructed in the same order and the comparison will pass.

The difference is whether order is part of its identity. A dict is still just a set of pairs, not a list of them. It just happens that it also guarantees now that if you _iterate_ over the set you'll walk the keys in insertion order.