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This is a solid argument for why you should have more datatypes available to you. If your program relies on an insertion order, say so. If anyone ever moves to another implementation, they will thank you for it.





Ordered dictionaries already existed as a separate type. Much of the gain was in the use of dicts for core language features.

In particular, Python 3.6 guarantees that the order in which class attributes are defined is preserved, and that functions which take variadic keyword arguments receive them in the order in which they were passed. It permits other implementations to use types other than dict to accomplish that.

Dataclasses make use of ordering of dictionaries in a subtle way. If you write:

  class Foo:
      bar: int
      baz: str
Then Foo.__annotations__ is a dictionary {'bar': int, 'baz': str}. The @dataclass decorator transforms that into standard boilerplate, and it needs to know the order to do that.

And this is all the more reason using a type would make sense. Curious why things use ordered? Look at all the places that declare they need ordered. :)

You don't know in advance when ordering might be useful, though.

Class __annotations__ was new in 3.6. For its original use there's no need for ordering. They were ordered, because dicts were ordered, but only as an implementation detail.

Dataclasses were added to 3.7, after 3.6's features made a nice syntax possible. If __annotations__ hadn't happened to be ordered already then I would guess it wouldn't have been made ordered just for dataclasses - dataclasses just wouldn't have existed.

Making everything ordered in one go opens up possibilities you haven't even thought of yet.


That argument cuts both ways. You don't know when the benefits of random will be there...

As soon as you do something that cares about order, state how it is derived. Sometimes, insertion order is right. Sometimes, not.

Don't get me wrong alists are nice. And order def matters to those. But it is part of their definition. And reinsertion changes the order in obvious ways. Not even clear what it does to just "dict".

Now, I will concede this is overblown. Life will easily go on.


It's extra annoying because collections.OrderedDict has been in the standard library for ages.

I fail to see what's annoying how. OrderedDict provide features for manipulating ordering, but they are expensive and slower. dict initially became ordered as a consequence of implementation details changes, and that was considered useful enough (or likely enough to trigger compatibility issues with third party implementation) that the core team decided to standardise it rather than break it (one of the advantages of the new implementation is iteration performances, shuffling iteration would probably have slowed it back down more than the old implementation)

Annoying is that it is not obvious why the two exist, by their name. They are both ordered. One is orderable in that you can change is order. I would not guess that looking at this.

For a language that prides itself on being readable, that is an amusing quirk.




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