[`pyupgrade`] Fix false positive for `TypeVar` with default on Python <3.13 (`UP046`,`UP047`) by prakhar1144 · Pull Request #21045 · astral-sh/ruff

prakhar1144 · 2025-10-23T13:22:31Z

Summary

Type default for Type parameter was added in Python 3.13 (PEP 696).

typing_extensions.TypeVar backports the default argument to earlier versions.

UP046 & UP047 were getting triggered when typing_extensions.TypeVar with default argument was used on python version < 3.13

It shouldn't be triggered for python version < 3.13

This commit fixes the bug by adding a python version check before triggering them.

Fixes #20929.

Test Plan

Manual testing 1

As the issue author pointed out in #20929 (comment), ran the following on main branch:

% cargo run -p ruff -- check ../efax/ --target-version py312 --no-cache

Output

   Compiling ruff_linter v0.14.1 (/Users/prakhar/ruff/crates/ruff_linter)
   Compiling ruff v0.14.1 (/Users/prakhar/ruff/crates/ruff)
   Compiling ruff_graph v0.1.0 (/Users/prakhar/ruff/crates/ruff_graph)
   Compiling ruff_workspace v0.0.0 (/Users/prakhar/ruff/crates/ruff_workspace)
   Compiling ruff_server v0.2.2 (/Users/prakhar/ruff/crates/ruff_server)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 6.72s
     Running `target/debug/ruff check ../efax/ --target-version py312 --no-cache`
UP046 Generic class `ExpectationParametrization` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/expectation_parametrization.py:17:48
   |
17 | class ExpectationParametrization(Distribution, Generic[NP]):
   |                                                ^^^^^^^^^^^
18 |     """The expectation parametrization of an exponential family distribution.
   |
help: Use type parameters

UP046 Generic class `ExpToNat` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/mixins/exp_to_nat/exp_to_nat.py:27:68
   |
26 | @dataclass
27 | class ExpToNat(ExpectationParametrization[NP], SimpleDistribution, Generic[NP]):
   |                                                                    ^^^^^^^^^^^
28 |     """This mixin implements the conversion from expectation to natural parameters.
   |
help: Use type parameters

UP046 Generic class `HasEntropyEP` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/mixins/has_entropy.py:25:20
   |
23 |                    HasEntropy,
24 |                    JaxAbstractClass,
25 |                    Generic[NP]):
   |                    ^^^^^^^^^^^
26 |     @abstract_jit
27 |     @abstractmethod
   |
help: Use type parameters

UP046 Generic class `HasEntropyNP` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/mixins/has_entropy.py:64:20
   |
62 | class HasEntropyNP(NaturalParametrization[EP],
63 |                    HasEntropy,
64 |                    Generic[EP]):
   |                    ^^^^^^^^^^^
65 |     @jit
66 |     @final
   |
help: Use type parameters

UP046 Generic class `NaturalParametrization` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/natural_parametrization.py:43:30
   |
41 | class NaturalParametrization(Distribution,
42 |                              JaxAbstractClass,
43 |                              Generic[EP, Domain]):
   |                              ^^^^^^^^^^^^^^^^^^^
44 |     """The natural parametrization of an exponential family distribution.
   |
help: Use type parameters

UP046 Generic class `Structure` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/efax/_src/structure/structure.py:31:17
   |
30 | @dataclass
31 | class Structure(Generic[P]):
   |                 ^^^^^^^^^^
32 |     """This class generalizes the notion of type for Distribution objects.
   |
help: Use type parameters

UP046 Generic class `DistributionInfo` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/efax/tests/distribution_info.py:20:24
   |
20 | class DistributionInfo(Generic[NP, EP, Domain]):
   |                        ^^^^^^^^^^^^^^^^^^^^^^^
21 |     def __init__(self, dimensions: int = 1, safety: float = 0.0) -> None:
22 |         super().__init__()
   |
help: Use type parameters

Found 7 errors.
No fixes available (7 hidden fixes can be enabled with the `--unsafe-fixes` option).

Running it after the changes:

ruff % cargo run -p ruff -- check ../efax/ --target-version py312 --no-cache
   Compiling ruff_linter v0.14.1 (/Users/prakhar/ruff/crates/ruff_linter)
   Compiling ruff v0.14.1 (/Users/prakhar/ruff/crates/ruff)
   Compiling ruff_graph v0.1.0 (/Users/prakhar/ruff/crates/ruff_graph)
   Compiling ruff_workspace v0.0.0 (/Users/prakhar/ruff/crates/ruff_workspace)
   Compiling ruff_server v0.2.2 (/Users/prakhar/ruff/crates/ruff_server)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 7.86s
     Running `target/debug/ruff check ../efax/ --target-version py312 --no-cache`
All checks passed!

Manual testing 2

Ran the check on the following script (mainly to verify UP047):

from __future__ import annotations                                                                                                                                                    

from typing import Generic

from typing_extensions import TypeVar

T = TypeVar("T", default=int)


def generic_function(var: T) -> T:
    return var


Q = TypeVar("Q", default=str)


class GenericClass(Generic[Q]):
    var: Q

On main branch:

ruff % cargo run -p ruff -- check ~/up046.py --target-version py312 --preview --no-cache

Output

   Compiling ruff_linter v0.14.1 (/Users/prakhar/ruff/crates/ruff_linter)
   Compiling ruff v0.14.1 (/Users/prakhar/ruff/crates/ruff)
   Compiling ruff_graph v0.1.0 (/Users/prakhar/ruff/crates/ruff_graph)
   Compiling ruff_workspace v0.0.0 (/Users/prakhar/ruff/crates/ruff_workspace)
   Compiling ruff_server v0.2.2 (/Users/prakhar/ruff/crates/ruff_server)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 7.43s
     Running `target/debug/ruff check /Users/prakhar/up046.py --target-version py312 --preview --no-cache`
UP047 Generic function `generic_function` should use type parameters
  --> /Users/prakhar/up046.py:10:5
   |
10 | def generic_function(var: T) -> T:
   |     ^^^^^^^^^^^^^^^^^^^^^^^^
11 |     return var
   |
help: Use type parameters

UP046 Generic class `GenericClass` uses `Generic` subclass instead of type parameters
  --> /Users/prakhar/up046.py:17:20
   |
17 | class GenericClass(Generic[Q]):
   |                    ^^^^^^^^^^
18 |     var: Q
   |
help: Use type parameters

Found 2 errors.
No fixes available (2 hidden fixes can be enabled with the `--unsafe-fixes` option).

After the fix (this branch):

ruff % cargo run -p ruff -- check ~/up046.py --target-version py312 --preview --no-cache
   Compiling ruff_linter v0.14.1 (/Users/prakhar/ruff/crates/ruff_linter)
   Compiling ruff v0.14.1 (/Users/prakhar/ruff/crates/ruff)
   Compiling ruff_graph v0.1.0 (/Users/prakhar/ruff/crates/ruff_graph)
   Compiling ruff_workspace v0.0.0 (/Users/prakhar/ruff/crates/ruff_workspace)
   Compiling ruff_server v0.2.2 (/Users/prakhar/ruff/crates/ruff_server)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 7.40s
     Running `target/debug/ruff check /Users/prakhar/up046.py --target-version py312 --preview --no-cache`
All checks passed!

github-actions · 2025-10-23T18:31:20Z

`ruff-ecosystem` results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

ntBre

Thank you! The code change and new comments look great, but would you mind converting your manual tests into regression tests in the repo?

If you already have separate Python files, they would fit nicely as new test cases alongside files like UP046_1.py and test_case entries here:

ruff/crates/ruff_linter/src/rules/pyupgrade/mod.rs

Lines 114 to 126 in 83a3bc4

    
           #[test_case(Rule::NonPEP695GenericFunction, Path::new("UP047.py"))] 
        
           #[test_case(Rule::PrivateTypeParameter, Path::new("UP049_0.py"))] 
        
           #[test_case(Rule::PrivateTypeParameter, Path::new("UP049_1.py"))] 
        
           #[test_case(Rule::UselessClassMetaclassType, Path::new("UP050.py"))] 
        
           fn rules(rule_code: Rule, path: &Path) -> Result<()> { 
        
               let snapshot = path.to_string_lossy().to_string(); 
        
               let diagnostics = test_path( 
        
                   Path::new("pyupgrade").join(path).as_path(), 
        
                   &settings::LinterSettings::for_rule(rule_code), 
        
               )?; 
        
               assert_diagnostics!(snapshot, diagnostics); 
        
               Ok(()) 
        
           }

Although you may need a separate test function so that you can set the version like we do here:

ruff/crates/ruff_linter/src/rules/pyupgrade/mod.rs

Line 244 in 83a3bc4

unresolved_target_version: PythonVersion::PY37.into(),

prakhar1144 · 2025-10-27T07:14:56Z

Thanks for the review!

As an update - I got busy with festivals around; I plan to complete this in the next 2-3 days.

….13 (`UP046`,`UP047`) Type default for Type parameter was added in Python 3.13 (PEP 696). `typing_extensions.TypeVar` backports the default argument to earlier versions. `UP046` & `UP047` were getting triggered when typing_extensions.TypeVar with `default` argument was used on python version < 3.13 It shouldn't be triggered for python version < 3.13 This commit fixes the bug by adding a python version check before triggering them. Fixes astral-sh#20929. Signed-off-by: Prakhar Pratyush <[email protected]>

prakhar1144 · 2025-10-29T22:44:01Z

@ntBre I've added tests. Ready to review.

ntBre

This is great, thank you!

* origin/main: (21 commits) [ty] Update "constraint implication" relation to work on constraints between two typevars (#21068) [`flake8-type-checking`] Fix `TC003` false positive with `future-annotations` (#21125) [ty] Fix lookup of `__new__` on instances (#21147) Fix syntax error false positive on nested alternative patterns (#21104) [`pyupgrade`] Fix false positive for `TypeVar` with default on Python <3.13 (`UP046`,`UP047`) (#21045) [ty] Reachability and narrowing for enum methods (#21130) [ty] Use `range` instead of custom `IntIterable` (#21138) [`ruff`] Add support for additional eager conversion patterns (`RUF065`) (#20657) [`ruff-ecosystem`] Fix CLI crash on Python 3.14 (#21092) [ty] Infer type of `self` for decorated methods and properties (#21123) [`flake8-bandit`] Fix correct example for `S308` (#21128) [ty] Dont provide goto definition for definitions which are not reexported in builtins (#21127) [`airflow`] warning `airflow....DAG.create_dagrun` has been removed (`AIR301`) (#21093) [ty] follow the breaking API changes made in salsa-rs/salsa#1015 (#21117) [ty] Rename `Type::into_nominal_instance` (#21124) [ty] Filter out "unimported" from the current module [ty] Add evaluation test for auto-import including symbols in current module [ty] Refactor `ty_ide` completion tests [ty] Render `import <...>` in completions when "label details" isn't supported [`refurb`] Preserve digit separators in `Decimal` constructor (`FURB157`) (#20588) ...

ntBre self-requested a review October 23, 2025 18:16

ntBre added bug Something isn't working rule Implementing or modifying a lint rule labels Oct 23, 2025

ntBre reviewed Oct 23, 2025

View reviewed changes

prakhar1144 force-pushed the fix-20929 branch from 056c130 to a559cb8 Compare October 29, 2025 22:36

ntBre approved these changes Oct 30, 2025

View reviewed changes

ntBre changed the title ~~[pyupgrade] Fix false positive for TypeVar with default on Python<3.13 (UP046,UP047)~~ [pyupgrade] Fix false positive for TypeVar with default on Python <3.13 (UP046,UP047) Oct 30, 2025

ntBre merged commit 10bda3d into astral-sh:main Oct 30, 2025
37 checks passed

BrewTestBot mentioned this pull request Oct 31, 2025

ruff 0.14.3 Homebrew/homebrew-core#252101

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[`pyupgrade`] Fix false positive for `TypeVar` with default on Python <3.13 (`UP046`,`UP047`)#21045

[`pyupgrade`] Fix false positive for `TypeVar` with default on Python <3.13 (`UP046`,`UP047`)#21045
ntBre merged 1 commit intoastral-sh:mainfrom
prakhar1144:fix-20929

prakhar1144 commented Oct 23, 2025

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	#[test_case(Rule::NonPEP695GenericFunction, Path::new("UP047.py"))]
	#[test_case(Rule::PrivateTypeParameter, Path::new("UP049_0.py"))]
	#[test_case(Rule::PrivateTypeParameter, Path::new("UP049_1.py"))]
	#[test_case(Rule::UselessClassMetaclassType, Path::new("UP050.py"))]
	fn rules(rule_code: Rule, path: &Path) -> Result<()> {
	let snapshot = path.to_string_lossy().to_string();
	let diagnostics = test_path(
	Path::new("pyupgrade").join(path).as_path(),
	&settings::LinterSettings::for_rule(rule_code),
	)?;
	assert_diagnostics!(snapshot, diagnostics);
	Ok(())
	}

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prakhar1144 commented Oct 23, 2025

Summary

Test Plan

Manual testing 1

Manual testing 2

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