Allow Python 3.15 as valid `target-version` value in preview #22419

Jkhall81 · 2026-01-06T16:04:50Z

Summary

Adds support for Python 3.15 to the Ruff workspace, gating it behind the preview flag with an unstable version warning as requested.

Part of #22230

astral-sh-bot · 2026-01-06T16:06:55Z

Diagnostic diff on typing conformance tests

No changes detected when running ty on typing conformance tests ✅

astral-sh-bot · 2026-01-06T16:07:51Z

`mypy_primer` results

Changes were detected when running on open source projects

pydantic (https://github.com/pydantic/pydantic)
- pydantic/fields.py:943:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:943:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:983:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:983:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1026:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:1026:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1066:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:1066:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1109:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:1109:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1148:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:1148:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1188:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`
+ pydantic/fields.py:1188:5: error[invalid-parameter-default] Default value of type `PydanticUndefinedType` is not assignable to annotated parameter type `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`
- pydantic/fields.py:1567:13: error[invalid-argument-type] Argument is incorrect: Expected `dict[str, int | float | str | ... omitted 3 union elements] | ((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) | None`, found `Top[dict[Unknown, Unknown]] | (((dict[str, int | float | str | ... omitted 3 union elements], /) -> None) & ~Top[dict[Unknown, Unknown]]) | None`
+ pydantic/fields.py:1567:13: error[invalid-argument-type] Argument is incorrect: Expected `dict[str, Divergent] | ((dict[str, Divergent], /) -> None) | None`, found `Top[dict[Unknown, Unknown]] | (((dict[str, Divergent], /) -> None) & ~Top[dict[Unknown, Unknown]]) | None`

xarray (https://github.com/pydata/xarray)
- xarray/core/dataarray.py:5757:16: error[invalid-return-type] Return type does not match returned value: expected `T_Xarray@map_blocks`, found `DataArray | Dataset`
+ xarray/core/dataarray.py:5757:16: error[invalid-return-type] Return type does not match returned value: expected `T_Xarray@map_blocks`, found `T_Xarray@map_blocks | DataArray | Dataset`
- xarray/core/dataset.py:8873:16: error[invalid-return-type] Return type does not match returned value: expected `T_Xarray@map_blocks`, found `DataArray | Dataset`
+ xarray/core/dataset.py:8873:16: error[invalid-return-type] Return type does not match returned value: expected `T_Xarray@map_blocks`, found `T_Xarray@map_blocks | DataArray | Dataset`

prefect (https://github.com/PrefectHQ/prefect)
- src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:461:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, Unknown | None]` is not awaitable
+ src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:461:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, None | Unknown]` is not awaitable
- src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:535:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, Unknown | None]` is not awaitable
+ src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:535:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, None | Unknown]` is not awaitable
- src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:610:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, Unknown | None]` is not awaitable
+ src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:610:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, None | Unknown]` is not awaitable
- src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:685:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, Unknown | None]` is not awaitable
+ src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:685:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, None | Unknown]` is not awaitable
- src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:760:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, Unknown | None]` is not awaitable
+ src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:760:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, None | Unknown]` is not awaitable
- src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:835:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, Unknown | None]` is not awaitable
+ src/integrations/prefect-dbt/prefect_dbt/cli/commands.py:835:21: error[invalid-await] `Unknown | None | Coroutine[Any, Any, None | Unknown]` is not awaitable

jax (https://github.com/google/jax)
- jax/_src/tree_util.py:302:31: error[invalid-argument-type] Argument to bound method `register_node` is incorrect: Expected `(Hashable, Iterable[object], /) -> T@register_pytree_node`, found `(_AuxData@register_pytree_node, _Children@register_pytree_node, /) -> T@register_pytree_node`
- jax/_src/tree_util.py:305:31: error[invalid-argument-type] Argument to bound method `register_node` is incorrect: Expected `(Hashable, Iterable[object], /) -> T@register_pytree_node`, found `(_AuxData@register_pytree_node, _Children@register_pytree_node, /) -> T@register_pytree_node`
- jax/_src/tree_util.py:308:31: error[invalid-argument-type] Argument to bound method `register_node` is incorrect: Expected `(Hashable, Iterable[object], /) -> T@register_pytree_node`, found `(_AuxData@register_pytree_node, _Children@register_pytree_node, /) -> T@register_pytree_node`
- Found 2808 diagnostics
+ Found 2805 diagnostics

pandas-stubs (https://github.com/pandas-dev/pandas-stubs)
+ pandas-stubs/_typing.pyi:1232:16: warning[unused-ignore-comment] Unused blanket `type: ignore` directive
- Found 5155 diagnostics
+ Found 5156 diagnostics

core (https://github.com/home-assistant/core)
+ homeassistant/util/variance.py:47:12: error[invalid-return-type] Return type does not match returned value: expected `(**_P@ignore_variance) -> _R@ignore_variance`, found `_Wrapped[_P@ignore_variance, _R@ignore_variance | int | float | datetime, _P@ignore_variance, _R@ignore_variance | int | float | datetime]`
- Found 14474 diagnostics
+ Found 14475 diagnostics

No memory usage changes detected ✅

MichaReiser · 2026-01-06T16:12:25Z

crates/ruff_python_ast/src/python_version.rs

    pub const fn latest_ty() -> Self {
        // Make sure to update the default value for `EnvironmentOptions::python_version` when bumping this version.
-        Self::PY314
+        Self::PY315


We should not change latest or latest_ty before we have stable Python 3.15 support

latest and latest_ty set back to 314.

astral-sh-bot · 2026-01-06T16:17:30Z

`ruff-ecosystem` results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

Formatter (stable)

✅ ecosystem check detected no format changes.

Formatter (preview)

✅ ecosystem check detected no format changes.

amyreese · 2026-01-06T16:22:56Z

Rule Update (RUF017): Implemented a version gate for quadratic-list-summation. Per PEP 798, sum() is now efficient for list-of-lists in Python 3.15, making this lint redundant for newer targets.

Is this just a byproduct of the changes from that PEP? I don't see anything about sum() mentioned in it.

amyreese · 2026-01-06T16:50:47Z

Perhaps we should split out the RUF017 changes to a separate PR? And maybe find better toy examples that demonstrate the issue? On my Mac, it actually shows the opposite result for me, with sum() being faster than reduce() on 3.10 and 3.12, and roughly equivalent on 3.14 and 3.15... 🤔

3.10:

amethyst@lunatone ~ » uvx python3.10 -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]' 'sum(data, [])'
5000000 loops, best of 5: 72.6 nsec per loop

amethyst@lunatone ~ » uvx python3.10 -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]' 'functools.reduce(operator.iadd, data, [])'
5000000 loops, best of 5: 85.1 nsec per loop

3.12:

amethyst@lunatone ~ » uvx python3.12 -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]' 'sum(data, [])'
5000000 loops, best of 5: 62.8 nsec per loop

amethyst@lunatone ~ » uvx python3.12 -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]' 'functools.reduce(operator.iadd, data, [])'
5000000 loops, best of 5: 84.4 nsec per loop

3.14:

amethyst@lunatone ~ » uvx python3.14 -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]' 'sum(data, [])'
5000000 loops, best of 5: 73.5 nsec per loop

amethyst@lunatone ~ » uvx python3.14 -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]' 'functools.reduce(operator.iadd, data, [])'
5000000 loops, best of 5: 75.3 nsec per loop

dylwil3 · 2026-01-06T17:20:43Z

On my Mac, it actually shows the opposite result for me

Maybe the list of lists was too small to see the difference?

❯ uvx python3.12 -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]*100' 'sum(data, [])'
2000 loops, best of 5: 119 usec per loop

❯ uvx python3.12 -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]*100' 'functools.reduce(operator.iadd, data, [])'
50000 loops, best of 5: 5.44 usec per loop

dylwil3 · 2026-01-06T17:40:39Z

Rule Update (RUF017): Implemented a version gate for quadratic-list-summation. Per PEP 798, sum() is now efficient for list-of-lists in Python 3.15, making this lint redundant for newer targets.

Is this just a byproduct of the changes from that PEP? I don't see anything about sum() mentioned in it.

I'm also confused. Neither the PEP in question nor its (unmerged) implementation touches anything to do with sum, right? Am I missing something?

Here's what I get building CPython with configurations ./configure --enable-optimizations --with-lto off the branch implementing PEP 798:

❯ ./python.exe --version
Python 3.15.0a3+

❯ ./python.exe -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]*100' 'sum(data, [])'
2000 loops, best of 5: 124 usec per loop

❯ ./python.exe -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]*100' 'functools.reduce(operator.iadd, data, [])'
50000 loops, best of 5: 6.04 usec per loop

❯ ./python.exe -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]*100' '[x for l in data for x in l]'
50000 loops, best of 5: 7.55 usec per loop

❯ ./python.exe -m timeit -s 'import operator, functools; data = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]*100' '[*x for x in data]'
50000 loops, best of 5: 4.82 usec per loop

So it doesn't look like sum is magically fast now. On the other hand, the PEP 798 syntax is now fastest!

Don't we want to keep the rule but just change the autofix?

Jkhall81 · 2026-01-06T17:51:17Z

Thanks for the benchmarks, @dylwil3. Looks like I misinterpreted the impact of PEP 798 on sum().

Just to confirm my understanding is correct for the next steps:

Remove the version gate so RUF017 stays active for 3.15.
Update the suggested fix for 3.15+ targets to use the new [*x for x in data] syntax instead of reduce.

Does that cover everything?

amyreese · 2026-01-06T17:55:00Z

Let's split the changes to RUF017 into a separate PR, and leave this one as just adding support for 3.15.

dylwil3 · 2026-01-06T17:59:45Z

Agreed. And could you maybe add something to preview.rs and emit a warning when preview is not enabled, as was done for 3.14 support before it was stabilized? See #17647 for prior art

Jkhall81 requested review from MichaReiser, carljm, dcreager and sharkdp as code owners January 6, 2026 16:04

MichaReiser reviewed Jan 6, 2026

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amyreese added the python315 label Jan 6, 2026

Jkhall81 force-pushed the fix/ruf017-pep798 branch from 6580de1 to 4ea3773 Compare January 6, 2026 16:36

Jkhall81 force-pushed the fix/ruf017-pep798 branch from 4ea3773 to d8c9883 Compare January 6, 2026 17:04

Jkhall81 force-pushed the fix/ruf017-pep798 branch from d8c9883 to dc74ac4 Compare January 6, 2026 17:23

Jkhall81 force-pushed the fix/ruf017-pep798 branch 2 times, most recently from b815682 to 615ac75 Compare January 6, 2026 19:12

feat(ruff): add Python 3.15 support and retire RUF017

fddc510

Jkhall81 force-pushed the fix/ruf017-pep798 branch from 615ac75 to fddc510 Compare January 6, 2026 19:25

AlexWaygood removed request for carljm, dcreager and sharkdp January 6, 2026 20:40

amyreese approved these changes Jan 6, 2026

View reviewed changes

amyreese requested a review from ntBre January 6, 2026 21:05

amyreese changed the title ~~feat(ruff): add Python 3.15 support and retire RUF017~~ feat(ruff): add Python 3.15 support Jan 6, 2026

dylwil3 added the configuration Related to settings and configuration label Jan 6, 2026

MichaReiser changed the title ~~feat(ruff): add Python 3.15 support~~ Allow Python 3.15 as valid target-version value in preview Jan 7, 2026

MichaReiser approved these changes Jan 7, 2026

View reviewed changes

MichaReiser merged commit 3b61da0 into astral-sh:main Jan 7, 2026
72 of 76 checks passed

BrewTestBot mentioned this pull request Jan 8, 2026

ruff 0.14.11 Homebrew/homebrew-core#261902

Merged

Allow Python 3.15 as valid target-version value in preview #22419

Allow Python 3.15 as valid target-version value in preview #22419

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Diagnostic diff on typing conformance tests

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mypy_primer results

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ruff-ecosystem results

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Formatter (preview)

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Allow Python 3.15 as valid `target-version` value in preview #22419

Allow Python 3.15 as valid `target-version` value in preview #22419

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