`tuple[*Ts]` subtype with extra type parameter not gradually assignable to itself
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Description
This demonstrates the issue:
from typing import Any
class Array[DataT, *ShapeTs](tuple[*ShapeTs]): ...
type Float2D = Array[float, *tuple[int, int]] # or Array[float, int, int]
type FloatND = Array[float, *tuple[Any, ...]]
def from_2d(a: Float2D) -> FloatND:
return a # mypy: ✅, pyright: ✅
def into_2d(a: FloatND) -> Float2D:
return a # mypy: ❌, pyright: ✅
https://mypy-play.net/?mypy=latest&python=3.13&flags=strict&gist=1b95c702df6de35fa3f61aa7b5dfef16
Without the additional DataT typar, the false positive disappears
from typing import Any
class Array[*ShapeTs](tuple[*ShapeTs]): ...
type Float2D = Array[*tuple[int, int]] # or Array[int, int]
type FloatND = Array[*tuple[Any, ...]]
def from_2d(a: Float2D) -> FloatND:
return a # mypy: ✅, pyright: ✅
def into_2d(a: FloatND) -> Float2D:
return a # mypy: ✅, pyright: ✅
https://mypy-play.net/?mypy=latest&python=3.13&flags=strict&gist=be0dfedeb0e7ed14da359cd52d2901e7
The issue also disappears when tuple is no longer a base class
from typing import Any
class Array[float, *ShapeTs]: ...
type Float2D = Array[float, *tuple[int, int]] # or Array[float, int, int]
type FloatND = Array[float, *tuple[Any, ...]]
def from_2d(a: Float2D) -> FloatND:
return a # mypy: ✅, pyright: ✅
def into_2d(a: FloatND) -> Float2D:
return a # mypy: ✅, pyright: ✅
https://mypy-play.net/?mypy=latest&python=3.13&flags=strict&gist=a1439e7c3037239bc4663b981534fb17
Potentially related issues:
- #18665
- #19106
- #19109
- #19110
- #19860
- #19858
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the two Python reproductions in the linked mypy-play examples with mypy 3.13 strict settings, comparing the from_2d and into_2d assignments and the variants without DataT or the tuple base class. Review related issues #18665, #19106, #19109, #19110, #19860, and #19858; done means the problematic assignment is handled consistently without breaking the cases that already pass.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100