uv add --dev ty
uv run ty check
All projects are typed. Every function and method gets a full signature — parameters and return type — in both src/ and tests/. No exceptions for "private" helpers, no "add them later". ty check runs clean on every commit; CI fails on type errors.
- Return
-> Noneis explicit, not optional. - Class attributes get annotations (
name: str), not just__init__parameters. - Tests count:
def test_foo() -> None:.
Modern syntax only (Python 3.14+):
# Yes
def fetch(ids: list[int]) -> dict[str, Item] | None: ...
# No — legacy
from typing import List, Dict, Optional
def fetch(ids: List[int]) -> Optional[Dict[str, Item]]: ...list[int], dict[str, X], X | None work without imports on 3.9+ for annotations and 3.10+ for runtime. On 3.14 everything works everywhere.
ty fallback: if ty check can't handle something your project legitimately needs (rare but happens with complex Protocols, PEP 695 generics edge cases, or plugin-heavy frameworks), swap ty for mypy on that project: uv remove ty && uv add --dev mypy, replace [tool.ty] with [tool.mypy], and note the swap in the README. Not a defeat; a documented escape hatch.
Don't use # type: ignore without a specific rule: # type: ignore[arg-type], not bare # type: ignore. Bare ignores hide new errors forever.