Made parameters of collections.abc members positional only

[randolf-scholz]

Fixes #14071

It doesn't seem like this will be fixed in CPython (python/cpython#135312), so we should at least fix this in the stubs to prevent false positives like this: mypy-playground

from collections.abc import Sequence

def null_count(seq: Sequence[int | None]) -> int:
    return seq.count(value=None)

null_count([1, None, 2])  # TypeError at runtime. (false negative)

Updated methods of the following types to only accept positional-only arguments:

• Sequence
• MutableSequence
• AbstractSet
• MutableSet
• KeysView
• ValuesView
• ItemsView

---

2026-01-20 (@srittau): Marked as deferred, until tests for 3.9 are dropped (#13782).

[randolf-scholz]

I guess the failure for 3.9 will resolve itself soon: #13782

[srittau]

LGTM, once we drop 3.9. (I've marked this as deferred until then.)

[randolf-scholz]

Did a rebase to resolve conflicts (slice got updated and _from_iterable added).

Additionally:

• made _from_iterable also positional only (it is an arbitrary name)
• made ABCMeta.{__instancecheck__, __subclasscheck__} positional only

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

cwltool (https://github.com/common-workflow-language/cwltool)
+ cwltool/update.py: note: In function "v1_2to1_3dev1":
+ cwltool/update.py:55:25: error: Unexpected keyword argument "index" for "pop" of "MutableSequence"  [call-arg]
+ ...typeshed_to_test/stdlib/typing.pyi:698:5: note: "pop" of "MutableSequence" defined here

pydantic (https://github.com/pydantic/pydantic)
- pydantic/_internal/_model_construction.py:308: error: Incompatible types in assignment (expression has type "Callable[[Any], bool]", base class "ABCMeta" defined the type as "def __instancecheck__(cls, instance: Any) -> bool")  [assignment]
- pydantic/_internal/_model_construction.py:309: error: Incompatible types in assignment (expression has type "Callable[[type], bool]", base class "ABCMeta" defined the type as "def __subclasscheck__(cls, subclass: type) -> bool")  [assignment]

jax (https://github.com/google/jax)
+ jax/_src/util.py:826: error: Unused "type: ignore" comment  [unused-ignore]
+ jax/_src/util.py:827: error: Unused "type: ignore" comment  [unused-ignore]

[randolf-scholz]

nice, the ABCMeta change got rid of false positive here: https://github.com/pydantic/pydantic/blob/a910cae58661194d5a56b2f1300ebae9a8a747a3/pydantic/_internal/_model_construction.py#L308-L309

    __instancecheck__ = type.__instancecheck__  # pyright: ignore[reportAssignmentType]
    __subclasscheck__ = type.__subclasscheck__  # pyright: ignore[reportAssignmentType]