Make `re.Match` a well-rounded `Sequence` type

Feature or enhancement

Proposal:

It would be nice if the following worked as expected:

m = re.match(r"(a)(b)(c)", "abc")

assert isinstance(m, Sequence)
assert len(m) == 4
assert list(m) == ["abc", "a", "b", "c"]

abc, a, b, c = m
assert abc == "abc" and a == "a" and b == "b" and c == "c"

match re.match(r"(\d+)-(\d+)-(\d+)", "2025-05-07"):
    case [_, year, month, day]:
        assert year == "2025" and month == "05" and day == "07"

If you also work with Javascript this will feel very familiar:

let m = "abc".match(/(a)(b)(c)/)

console.log(m instanceof Array) // true
console.log(m.length) // 4
console.log(Array.from(m)) // [ 'abc', 'a', 'b', 'c' ]

let [abc, a, b, c] = m
console.log(abc) // abc
console.log(a) // a
console.log(b) // b
console.log(c) // c

Back in 2016, the re.Match object API was expanded to include __getitem__ as a shortcut for .group(...).

The goal was to improve usability and approachability by making re.Match objects fit a bit more seamlessly into python's core data model. Accessing groups via subscripting is now intuitive, but because re.Match objects only have a __getitem__ and no __len__, they can't be used as a proper Sequence type.

To me, this always felt a bit awkward. After digging up the original discussion, it seems like the reason why __len__ didn't make it was that it was still undecided whether the returned value should take into account group 0 or not.

Almost a decade later, as a user, the way I see it is that the __getitem__ implementation we're now used to suggests a regular Sequence type that also happens to transparently translate group names provided as subscript to their corresponding group index. In fact, this is actually how it works in the underlying C code.

With this in mind, we can simply define __len__ taking into account group 0, and we'll finally be able to enjoy coherent re.Match objects that behave as proper Sequence types.

Has this already been discussed elsewhere?

https://discuss.python.org/t/make-re-match-a-well-rounded-sequence-type/91039

Links to previous discussion of this feature:

Improve the usability of the match object named group API (https://github.com/python/cpython/commit/605bdae0780a1ff8a88b80e6e67f3f355fb2ddb4)

Linked PRs

• gh-133549

从 re.Match 入口点及其现有的 getitem 行为开始，然后阅读关于 group 0 和 Sequence 语义的相关讨论。将提案中的断言和模式匹配示例作为验收标准；完成意味着已确立预期的长度、迭代、解包和序列模式行为，且不存在未解决的 API 问题。