add as_sequence() method on dict views

[PrettyWood]

Hi and thank you for this amazing library! I'm trying to help @samuelcolvin on https://github.com/samuelcolvin/pydantic-core. Following #2358, it would be great to have at list a as_sequence() method on dict views to be able to easily get length, convert them to list, iterate...
I didn't want to add any other methods following @davidhewitt 's comment. Let's keep it simple for now :)

• an entry in CHANGELOG.md
• docs to all new functions and / or detail in the guide
• tests for all new or changed functions

[samuelcolvin]

LGTM 👍

[PrettyWood]

I don't know what's wrong on windows and if it's even related to this PR 🤔

[mejrs]

Thanks!

I don't know what's wrong on windows and if it's even related to this PR 🤔

Looks like The filename or extension is too long. (os error 206)...ugh. I don't know what's up with that.

[PrettyWood]

dankjewel @mejrs for the quick review! 🙏

[davidhewitt]

Hey, thanks for this.

I'm definitely willing to add some methods to these views to improve usability, although I'm not convinced .as_sequence() is strictly correct. This appears to break type-safety, as I don't think these collections are sequences:

>>> import collections
>>> isinstance({}.keys(), collections.abc.Sequence)
False

You can already make use of the fact these views implement Deref<Target=PyAny> to use .len(), .iter() etc.

If we add methods to these types I would guess the main motivation would either be:

• performance if there's a C API we can make use of
• remove need for PyResult<_> on .len() etc.

Is it possible that someone could subtype dict_keys (e.g.) and create a __len__ which raises an exception? I think so, in which case we have to make a judgement call whether a bespoke fn len() -> usize on these types would panic in that case. So far in PyO3 we've made the decision to return results in all such cases so as to minimise library-level panics.

[PrettyWood]

Ah you're absolutely right @davidhewitt! Thank you!
Since order is preserved, I thought dict views would be sequences but since they are not we can close this PR.

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At first I also added a len() method indeed to avoid having a Result type but I understand the judgement call.

Thanks again for this library!