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Please read the maintenance notes at the top of this file.

Please read the maintenance notes at the top of this file.

Will it be OK to add new ABCs (for example,ReversibleMapping andMutableReversibleMapping) and new keys, values, items views for them? I can create a new pull request for this.

Will it be OK to add new ABCs

That would work, but it doesn't seem worth it. There is almost zero benefit. These ABCs have been around a long time and no one has missed the reversible spec. Likely, this is because the concretedict class's reversible feature is rarely used.

In general, the ABCs are intentionally not full featured. The intent of the ABCs was to be a minimal spec. For example, MutableSet lacks union, intersection, and difference; the operators are supposed to suffice.

One other thought is that reversibility is only meaningful if the underlying mapping is ordered, but we have no way to specify or enforce an ordering requirement with ABCs so this would be on shaky ground.

That would work, but it doesn't seem worth it. There is almost zero benefit. These ABCs have been around a long time and no one has missed the reversible spec. Likely, this is because the concretedict class's reversible feature is rarely used.

In general, the ABCs are intentionally not full featured. The intent of the ABCs was to be a minimal spec. For example, MutableSet lacks union, intersection, and difference; the operators are supposed to suffice.

One other thought is that reversibility is only meaningful if the underlying mapping is ordered, but we have no way to specify or enforce an ordering requirement with ABCs so this would be on shaky ground.

So do you want to say that you will not merge this PR and PR with new ABCs?

I want to add reversibility because:

1. I think there should be ABC for ordered (hence reversible) mapping, like OrderedDict
2. I miss this feature for my project

See alsoGH-134863

dict andOrderedDict have reversed keys, values and items iterators, then, I think, ABC for ordered mapping should too (it can be a new ABC not to cause incompatibility, I read the maintenance notes).