inspect: Add positions attributes that will be new in 3.11

[JelleZijlstra]

python/cpython#91531

[hauntsaninja]

Defining __new__ looks cleaner than what I did for dis. Edit: it also happens to be what the runtime does

[AlexWaygood]

Defining __new__ looks cleaner than what I did for dis. Edit: it also happens to be what the runtime does

It does however break mypy 🙃

[JelleZijlstra]

hm, now I get stdlib/inspect.pyi:472: error: Cannot overwrite NamedTuple attribute "__new__" [misc]. Do we have a better technique or should we just type ignore it?

[AlexWaygood]

hm, now I get stdlib/inspect.pyi:472: error: Cannot overwrite NamedTuple attribute "__new__" [misc]. Do we have a better technique or should we just type ignore it?

We could do something similar to what I did with structseq classes in other modules. But I don't think there's any need, because (unlike with structseqs), there's no attributes on these classes that are ClassVars. And mypy can infer the types fine, even if it doesn't think it can, so I say: just type: ignore it away.

https://mypy-play.net/?mypy=latest&python=3.10&gist=2bdfa6f9cdc2bdd07c5d472bf4124ea5

[AlexWaygood]

On second thoughts, why don't we just mimic the runtime implementation exactly? It seems to work pretty well for tokenize.TokenInfo:

typeshed/stdlib/tokenize.pyi

Lines 324 to 333 in 7cbb579

	class _TokenInfo(NamedTuple):
	type: int
	string: str
	start: _Position
	end: _Position
	line: str
	class TokenInfo(_TokenInfo):
	@property
	def exact_type(self) -> int: ...

and it would mean we could override __new__ without a # type: ignore. It also means that we can annotate the positions attributes as settable instance variables, which they are at runtime in 3.11, even though all other attributes on Traceback and FrameInfo are read-only.

So in the 3.11 branch we would have:

if sys.version_info >= (3, 11):
    class _Traceback(NamedTuple):
        filename: str
        lineno: int
        function: str
        code_context: list[str] | None
        index: int | None  # type: ignore[assignment]

    class Traceback(_Traceback):
        positions: dis.Positions | None
        def __new__(
            cls: type[Self],
            filename: str,
            lineno: int,
            function: str,
            code_context: list[str] | None,
            index: int | None,
            *,
            positions: dis.Positions | None = ...,
        ) -> Self: ...

    class _FrameInfo(NamedTuple):
        frame: FrameType
        filename: str
        lineno: int
        function: str
        code_context: list[str] | None
        index: int | None  # type: ignore[assignment]

    class FrameInfo(_FrameInfo):
        positions: dis.Positions | None
        def __new__(
            cls: type[Self],
            frame: FrameType,
            filename: str,
            lineno: int,
            function: str,
            code_context: list[str] | None,
            index: int | None,
            *,
            positions: dis.Positions | None = ...,
        ) -> Self: ...

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉