ENH: Replace `NestedSequence` with a proper nested sequence protocol

1 files changed, 17 insertions, 5 deletions

diff --git a/numpy/array_api/_typing.py b/numpy/array_api/_typing.py
index 519e8463c..5e980b16f 100644
--- a/numpy/array_api/_typing.py
+++ b/numpy/array_api/_typing.py
@@ -6,6 +6,8 @@ annotations in the function signatures. The functions in the module are only
 valid for inputs that match the given type annotations.
 """
 
+from __future__ import annotations
+
 __all__ = [
     "Array",
     "Device",
@@ -16,7 +18,16 @@ __all__ = [
 ]
 
 import sys
-from typing import Any, Literal, Sequence, Type, Union, TYPE_CHECKING, TypeVar
+from typing import (
+    Any,
+    Literal,
+    Sequence,
+    Type,
+    Union,
+    TYPE_CHECKING,
+    TypeVar,
+    Protocol,
+)
 
 from ._array_object import Array
 from numpy import (
@@ -33,10 +44,11 @@ from numpy import (
     float64,
 )
 
-# This should really be recursive, but that isn't supported yet. See the
-# similar comment in numpy/typing/_array_like.py
-_T = TypeVar("_T")
-NestedSequence = Sequence[Sequence[_T]]
+_T_co = TypeVar("_T_co", covariant=True)
+
+class NestedSequence(Protocol[_T_co]):
+    def __getitem__(self, key: int, /) -> _T_co | NestedSequence[_T_co]: ...
+    def __len__(self, /) -> int: ...
 
 Device = Literal["cpu"]
 if TYPE_CHECKING or sys.version_info >= (3, 9):