Python 3.15 Support

[ntBre]

This is a tracking issue for Python 3.15 support.

PEP 810: Lazy imports

• UP026 needs lazy import support in libCST for fixes to work

  • Update LibCST-based fixes for Python 3.15 #28616

• TC001 - TC003 should not apply with lazy imports #25181

  • [flake8-type-checking] Prefer lazy imports over TYPE_CHECKING on 3.15+ (TC001, TC002, TC003) #28541

• Support __lazy_modules__ in lazy import rules #25170

  • Add support for __lazy_modules__ #28459

• [Infinite loop] TID254 when an import statement has conflicting laziness requirements #26450

  • [flake8-tidy-imports] Skip fixes for multi-member imports (TID254) #26584

• Conflict (infinite loop) between lazy-import-mismatch (TID254) and lazy-import-immediately-resolved (TID255) with lint.flake8-tidy-imports.require-lazy="all"` #25418

  • [flake8-tidy-imports] Prevent fix loop between TID254 and TID255 #28262

PEP 798: Unpacking in comprehensions

• Add full PEP 798 support #25104
• C411, C418, and C419 diagnose the new unpacking comprehensions but cannot autofix them because the LibCST-based fixers do not support the syntax yet
  • Update LibCST-based fixes for Python 3.15 #28616

Unicode 17

• Update Rust crate unicode-normalization to v0.1.25 #21229
• Update Rust crate unicode_names2 to v3 #26077
  • Normalize character alias lookup keys progval/unicode_names2#61
  • Add an alias-lookup API to support strict matching progval/unicode_names2#63

Parser

• Unary plus is now accepted in match literal patterns, mirroring the existing support for unary minus. Our existing parse error should become a version-related syntax error.
  • Allow unary plus in match patterns on Python 3.15 #28231

Standard library updates

• Update stdlibs with 3.15 #21119
  • PEP 814: Add frozendict built-in type
  • PEP 661: Add sentinel built-in type
  • PEP 799: A dedicated profiling package

Other rule changes

• RUF039 and RUF055 should know about re.prefixmatch
  • [ruff] Recognize re.prefixmatch (RUF039, RUF055) #28311
• ImportCycleError is incorrectly classified as a 3.13 builtin in PLW0133
  • [pylint] Gate ImportCycleError on Python 3.15 (PLW0133) #28310
• Ruff should recognize slice and frozendict as generic types so their quoted type arguments are analyzed correctly.
  • Recognize slice and frozendict generics #28477
  • Python 3.15 language changes, including generic slice
  • PEP 814: Add frozendict built-in type
  • Current code: standard-library generic recognition
• Deprecated typing.no_type_check_decorator() has been removed and should no longer be recommended by UP035
  • [pyupgrade] Stop recommending removed typing.no_type_check_decorator (UP035) #28475
• __cached__ is no longer initialized in Python 3.15 and should only be included in Ruff's magic globals for earlier target versions.
  • Stop defining __cached__ for Python 3.15 #28476
  • Python 3.15 language changes
  • Current code: unconditional magic globals and version-dependent magic globals
• typing.ByteString and collections.abc.ByteString have both been removed from their respective __all__s. It probably makes sense to drop the typing.ByteString -> collections.abc.ByteString recommendation from UP035 as well (but keep the collections.ByteString -> collections.abc.ByteString version, which is still helpful on older versions)
  • [pyupgrade] Stop recommending deprecated ByteString aliases (UP035) #28498
• Ruff should recognize quoted types in TypeForm[...] and TypeForm(...), avoiding false F401 diagnostics.
  • Recognize quoted types in typing.TypeForm #28507
  • PEP 747: Annotating type forms
  • Current code: generic recognition and typing-call classification
• TypeVarTuple now accepts bound, but UP040, UP046, and UP047 generate invalid syntax such as [*Ts: int]. These conversions should be skipped while the bound's typing semantics remain unspecified.
  • [pyupgrade] Skip TypeVarTuple and ParamSpec conversions with bounds or constraints (UP040, UP046, UP047) #28505
  • Python 3.15 typing changes
  • Current code: shared PEP 695 type-parameter rendering
• RUF064 should check the new parent_mode argument to os.makedirs and Path.mkdir. PTH103 should preserve it when converting os.makedirs calls to Path.mkdir.
  • [ruff, flake8-use-pathlib] Support parent_mode (RUF064, PTH103) #28528
  • Python documentation: os.makedirs and Path.mkdir
  • Current code: permission argument detection and os.makedirs fix validation
• UP013 should preserve the new TypedDict closed and extra_items arguments when converting to class syntax. Quoted types in class-based extra_items arguments should also count as uses of their imports, avoiding false F401 diagnostics.
  • Recognize PEP-728 TypedDict class keywords #28533
  • PEP 728: TypedDict with typed extra items
  • Current code: TypedDict conversion and class analysis

Rule stabilizations

• lazy-import-mismatch (TID254)
• lazy-import-immediately-resolved (TID255)
• os-path-commonprefix (RUF071)

Misc

• Rebuild for python 3.15 conda-forge/ruff-feedstock#363
• Bump the language classifier in pyproject.toml
• Update default and latest Python versions
  • 3.10 is reaching EOL
  • See Update default and latest Python versions for 3.14 #20725 for last year's bump

Potential lint rules

These shouldn't block the release, but could be interesting.

• Support and lints for lazy imports in Python 3.15+ #21305

  This primarily tracks additional lints now, with the remaining adjustment to existing rules (point 2) tracked by TC001 - TC003 should not apply with lazy imports #25181.

• Prefer prefixmatch over match #24545

• Suggested optimizing refactors around bytearray.take_bytes