ENH: Free-threading support

.github/workflows/ci.yml

@@ -45,13 +45,18 @@ jobs:
           pixi run -e lint pyright
 
   checks:
-    name: Check ${{ matrix.environment }}
+    name: Test ${{ matrix.environment }}
     runs-on: ${{ matrix.runs-on }}
     needs: [pre-commit-and-lint]
     strategy:
       fail-fast: false
       matrix:
-        environment: [tests-py310, tests-py313, tests-numpy1, tests-backends]
+        environment:
+          - tests-py310
+          - tests-py313
+          - tests-numpy1
+          - tests-backends
+          - tests-nogil
         runs-on: [ubuntu-latest]
 
     steps:
@@ -66,9 +71,16 @@ jobs:
           environments: ${{ matrix.environment }}
 
       - name: Test package
+        # Save some time; also at the moment of writing coverage crashes on python 3.13t
+        if: ${{ matrix.environment != 'tests-nogil' }}
         run: pixi run -e ${{ matrix.environment }} tests-ci
 
+      - name: Test free-threading
+        if: ${{ matrix.environment == 'tests-nogil' }}
+        run: pixi run -e tests-nogil tests --parallel-threads=4
+
       - name: Upload coverage report
+        if: ${{ matrix.environment != 'tests-nogil' }}
         uses: codecov/codecov-action@18283e04ce6e62d37312384ff67231eb8fd56d24 # v5.4.3
         with:
           token: ${{ secrets.CODECOV_TOKEN }}

pyproject.toml

@@ -23,6 +23,7 @@ classifiers = [
   "Programming Language :: Python :: 3.11",
   "Programming Language :: Python :: 3.12",
   "Programming Language :: Python :: 3.13",
+  "Programming Language :: Python :: Free Threading :: 3 - Stable",
   "Typing :: Typed",
 ]
 dynamic = ["version"]
@@ -47,7 +48,6 @@ channels = ["https://prefix.dev/conda-forge"]
 platforms = ["linux-64", "osx-64", "osx-arm64", "win-64"]
 
 [tool.pixi.dependencies]
-python = ">=3.10,<3.14"
 array-api-compat = ">=1.12.0,<2"
 
 [tool.pixi.pypi-dependencies]
@@ -179,6 +179,15 @@ cupy = ">=13.4.1"
 # jaxlib = { version = "*", build = "cuda12*" }  # unavailable
 pytorch = { version = ">=2.7.0", build = "cuda12*" }
 
+[tool.pixi.feature.nogil.dependencies]
+python-freethreading = "~=3.13.0"
+pytest-run-parallel = ">=0.4.3"
+numpy = ">=2.3.0"
+# pytorch = "*"  # Not available on Python 3.13t yet
+dask-core = ">=2025.5.1"  # No distributed, tornado, etc.
+# sparse = "*"  # numba not available on Python 3.13t yet
+# jax = "*"  # ml_dtypes not available on Python 3.13t yet
+
 [tool.pixi.environments]
 default = { features = ["py313"], solve-group = "py313" }
 lint = { features = ["py313", "lint"], solve-group = "py313" }
@@ -197,7 +206,7 @@ tests-cuda = { features = ["py310", "tests", "backends", "cuda-backends"], solve
 # Ungrouped environments
 tests-numpy1 = ["py310", "tests", "numpy1"]
 tests-py310 = ["py310", "tests"]
-
+tests-nogil = ["nogil", "tests"]
 
 # pytest
 

src/array_api_extra/_lib/_backends.py

@@ -3,8 +3,14 @@
 from __future__ import annotations
 
 from enum import Enum
+from typing import Any
 
-__all__ = ["Backend"]
+import numpy as np
+import pytest
+
+__all__ = ["NUMPY_VERSION", "Backend"]
+
+NUMPY_VERSION = tuple(int(v) for v in np.__version__.split(".")[:3])  # pyright: ignore[reportUnknownArgumentType]
 
 
 class Backend(Enum):  # numpydoc ignore=PR02
@@ -30,12 +36,6 @@ class Backend(Enum):  # numpydoc ignore=PR02
     JAX = "jax.numpy"
     JAX_GPU = "jax.numpy:gpu"
 
-    def __str__(self) -> str:  # pyright: ignore[reportImplicitOverride]  # numpydoc ignore=RT01
-        """Pretty-print parameterized test names."""
-        return (
-            self.name.lower().replace("_gpu", ":gpu").replace("_readonly", ":readonly")
-        )
-
     @property
     def modname(self) -> str:  # numpydoc ignore=RT01
         """Module name to be imported."""
@@ -44,3 +44,29 @@ def modname(self) -> str:  # numpydoc ignore=RT01
     def like(self, *others: Backend) -> bool:  # numpydoc ignore=PR01,RT01
         """Check if this backend uses the same module as others."""
         return any(self.modname == other.modname for other in others)
+
+    def pytest_param(self) -> Any:
+        """
+        Backend as a pytest parameter
+
+        Returns
+        -------
+        pytest.mark.ParameterSet
+        """
+        id_ = (
+            self.name.lower().replace("_gpu", ":gpu").replace("_readonly", ":readonly")
+        )
+
+        marks = []
+        if self.like(Backend.ARRAY_API_STRICT):
+            marks.append(
+                pytest.mark.skipif(
+                    NUMPY_VERSION < (1, 26),
+                    reason="array_api_strict is untested on NumPy <1.26",
+                )
+            )
+        if self.like(Backend.DASK, Backend.JAX):
+            # Monkey-patched by lazy_xp_function
+            marks.append(pytest.mark.thread_unsafe)
+
+        return pytest.param(self, id=id_, marks=marks)  # pyright: ignore[reportUnknownArgumentType]

src/array_api_extra/_lib/_lazy.py

@@ -343,7 +343,7 @@ def wrapper(
                 if as_numpy:
                     import numpy as np
 
-                    arg = cast(Array, np.asarray(arg))  # noqa: PLW2901
+                    arg = cast(Array, np.asarray(arg))  # pyright: ignore[reportInvalidCast] # noqa: PLW2901
             args_list.append(arg)
         assert device is not None
 

src/array_api_extra/testing.py

@@ -9,7 +9,7 @@
 import contextlib
 import enum
 import warnings
-from collections.abc import Callable, Iterator, Sequence
+from collections.abc import Callable, Generator, Iterator, Sequence
 from functools import wraps
 from types import ModuleType
 from typing import TYPE_CHECKING, Any, ParamSpec, TypeVar, cast
@@ -216,8 +216,11 @@ def test_myfunc(xp):
 
 
 def patch_lazy_xp_functions(
-    request: pytest.FixtureRequest, monkeypatch: pytest.MonkeyPatch, *, xp: ModuleType
-) -> None:
+    request: pytest.FixtureRequest,
+    monkeypatch: pytest.MonkeyPatch | None = None,
+    *,
+    xp: ModuleType,
+) -> contextlib.AbstractContextManager[None]:
     """
     Test lazy execution of functions tagged with :func:`lazy_xp_function`.
 
@@ -233,10 +236,15 @@ def patch_lazy_xp_functions(
     This function should be typically called by your library's `xp` fixture that runs
     tests on multiple backends::
 
-        @pytest.fixture(params=[numpy, array_api_strict, jax.numpy, dask.array])
-        def xp(request, monkeypatch):
-            patch_lazy_xp_functions(request, monkeypatch, xp=request.param)
-            return request.param
+        @pytest.fixture(params=[
+            numpy,
+            array_api_strict,
+            pytest.param(jax.numpy, marks=pytest.mark.thread_unsafe),
+            pytest.param(dask.array, marks=pytest.mark.thread_unsafe),
+        ])
+        def xp(request):
+            with patch_lazy_xp_functions(request, xp=request.param):
+                yield request.param
 
     but it can be otherwise be called by the test itself too.
 
@@ -245,18 +253,50 @@ def xp(request, monkeypatch):
     request : pytest.FixtureRequest
         Pytest fixture, as acquired by the test itself or by one of its fixtures.
     monkeypatch : pytest.MonkeyPatch
-        Pytest fixture, as acquired by the test itself or by one of its fixtures.
+        Deprecated
     xp : array_namespace
         Array namespace to be tested.
 
     See Also
     --------
     lazy_xp_function : Tag a function to be tested on lazy backends.
     pytest.FixtureRequest : `request` test function parameter.
+
+    Notes
+    -----
+    This context manager monkey-patches modules and as such is thread unsafe
+    on Dask and JAX. If you run your test suite with
+    `pytest-run-parallel <https://github.com/Quansight-Labs/pytest-run-parallel/>`_,
+    you should mark these backends with ``@pytest.mark.thread_unsafe``, as shown in
+    the example above.
     """
     mod = cast(ModuleType, request.module)
     mods = [mod, *cast(list[ModuleType], getattr(mod, "lazy_xp_modules", []))]
 
+    to_revert: list[tuple[ModuleType, str, object]] = []
+
+    def temp_setattr(mod: ModuleType, name: str, func: object) -> None:
+        """
+        Variant of monkeypatch.setattr, which allows monkey-patching only selected
+        parameters of a test so that pytest-run-parallel can run on the remainder.
+        """
+        assert hasattr(mod, name)
+        to_revert.append((mod, name, getattr(mod, name)))
+        setattr(mod, name, func)
+
+    if monkeypatch is not None:
+        warnings.warn(
+            (
+                "The `monkeypatch` parameter is deprecated and will be removed in a "
+                "future version. "
+                "Use `patch_lazy_xp_function` as a context manager instead."
+            ),
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        # Enable using patch_lazy_xp_function not as a context manager
+        temp_setattr = monkeypatch.setattr  # type: ignore[assignment]  # pyright: ignore[reportAssignmentType]
+
     def iter_tagged() -> (
         Iterator[tuple[ModuleType, str, Callable[..., Any], dict[str, Any]]]
     ):
@@ -279,13 +319,26 @@ def iter_tagged() -> (
             elif n is False:
                 n = 0
             wrapped = _dask_wrap(func, n)
-            monkeypatch.setattr(mod, name, wrapped)
+            temp_setattr(mod, name, wrapped)
 
     elif is_jax_namespace(xp):
         for mod, name, func, tags in iter_tagged():
             if tags["jax_jit"]:
                 wrapped = jax_autojit(func)
-                monkeypatch.setattr(mod, name, wrapped)
+                temp_setattr(mod, name, wrapped)
+
+    # We can't just decorate patch_lazy_xp_functions with
+    # @contextlib.contextmanager because it would not work with the
+    # deprecated monkeypatch when not used as a context manager.
+    @contextlib.contextmanager
+    def revert_on_exit() -> Generator[None]:
+        try:
+            yield
+        finally:
+            for mod, name, orig_func in to_revert:
+                setattr(mod, name, orig_func)
+
+    return revert_on_exit()
 
 
 class CountingDaskScheduler(SchedulerGetCallable):

tests/conftest.py

@@ -18,11 +18,10 @@
 T = TypeVar("T")
 P = ParamSpec("P")
 
-NUMPY_VERSION = tuple(int(v) for v in np.__version__.split(".")[2])
 np_compat = array_namespace(np.empty(0))  # type: ignore[arg-type]  # pyright: ignore[reportArgumentType]
 
 
-@pytest.fixture(params=tuple(Backend))
+@pytest.fixture(params=[b.pytest_param() for b in Backend])
 def library(request: pytest.FixtureRequest) -> Backend:  # numpydoc ignore=PR01,RT03
     """
     Parameterized fixture that iterates on all libraries.
@@ -112,7 +111,7 @@ def wrapper(*args: P.args, **kwargs: P.kwargs) -> T:  # numpydoc ignore=GL08
 
 @pytest.fixture
 def xp(
-    library: Backend, request: pytest.FixtureRequest, monkeypatch: pytest.MonkeyPatch
+    library: Backend, request: pytest.FixtureRequest
 ) -> Generator[ModuleType]:  # numpydoc ignore=PR01,RT03
     """
     Parameterized fixture that iterates on all libraries.
@@ -125,9 +124,6 @@ def xp(
         yield NumPyReadOnly()  # type: ignore[misc]  # pyright: ignore[reportReturnType]
         return
 
-    if library.like(Backend.ARRAY_API_STRICT) and NUMPY_VERSION < (1, 26):
-        pytest.skip("array_api_strict is untested on NumPy <1.26")
-
     xp = pytest.importorskip(library.modname)
     # Possibly wrap module with array_api_compat
     xp = array_namespace(xp.empty(0))
@@ -143,16 +139,15 @@ def xp(
             yield xp
         return
 
-    # On Dask and JAX, monkey-patch all functions tagged by `lazy_xp_function`
-    # in the global scope of the module containing the test function.
-    patch_lazy_xp_functions(request, monkeypatch, xp=xp)
-
     if library.like(Backend.JAX):
         _setup_jax(library)
     elif library.like(Backend.TORCH):
         _setup_torch(library)
 
-    yield xp
+    # On Dask and JAX, monkey-patch all functions tagged by `lazy_xp_function`
+    # in the global scope of the module containing the test function.
+    with patch_lazy_xp_functions(request, xp=xp):
+        yield xp
 
 
 def _setup_jax(library: Backend) -> None:
@@ -189,26 +184,27 @@ def _setup_torch(library: Backend) -> None:
         torch.set_default_device("cpu")
 
 
-@pytest.fixture(params=[Backend.DASK])  # Can select the test with `pytest -k dask`
+# Can select the test with `pytest -k dask`
+@pytest.fixture(params=[Backend.DASK.pytest_param()])
 def da(
-    request: pytest.FixtureRequest, monkeypatch: pytest.MonkeyPatch
-) -> ModuleType:  # numpydoc ignore=PR01,RT01
+    request: pytest.FixtureRequest,
+) -> Generator[ModuleType]:  # numpydoc ignore=PR01,RT01
     """Variant of the `xp` fixture that only yields dask.array."""
     xp = pytest.importorskip("dask.array")
     xp = array_namespace(xp.empty(0))
-    patch_lazy_xp_functions(request, monkeypatch, xp=xp)
-    return xp
+    with patch_lazy_xp_functions(request, xp=xp):
+        yield xp
 
 
-@pytest.fixture(params=[Backend.JAX, Backend.JAX_GPU])
+@pytest.fixture(params=[Backend.JAX.pytest_param(), Backend.JAX_GPU.pytest_param()])
 def jnp(
-    request: pytest.FixtureRequest, monkeypatch: pytest.MonkeyPatch
-) -> ModuleType:  # numpydoc ignore=PR01,RT01
+    request: pytest.FixtureRequest,
+) -> Generator[ModuleType]:  # numpydoc ignore=PR01,RT01
     """Variant of the `xp` fixture that only yields jax.numpy."""
     xp = pytest.importorskip("jax.numpy")
     _setup_jax(request.param)
-    patch_lazy_xp_functions(request, monkeypatch, xp=xp)
-    return xp
+    with patch_lazy_xp_functions(request, xp=xp):
+        yield xp
 
 
 @pytest.fixture(params=[Backend.TORCH, Backend.TORCH_GPU])

tests/test_at.py

@@ -178,7 +178,7 @@ def test_copy_invalid():
 
 
 def test_xp():
-    a = cast(Array, np.asarray([1, 2, 3]))
+    a = cast(Array, np.asarray([1, 2, 3]))  # pyright: ignore[reportInvalidCast]
     _ = at(a, 0).set(4, xp=np)
     _ = at(a, 0).add(4, xp=np)
     _ = at(a, 0).subtract(4, xp=np)

tests/test_funcs.py

@@ -27,15 +27,13 @@
     setdiff1d,
     sinc,
 )
-from array_api_extra._lib._backends import Backend
+from array_api_extra._lib._backends import NUMPY_VERSION, Backend
 from array_api_extra._lib._testing import xp_assert_close, xp_assert_equal
 from array_api_extra._lib._utils._compat import device as get_device
 from array_api_extra._lib._utils._helpers import eager_shape, ndindex
 from array_api_extra._lib._utils._typing import Array, Device
 from array_api_extra.testing import lazy_xp_function
 
-from .conftest import NUMPY_VERSION
-
 lazy_xp_function(apply_where)
 lazy_xp_function(atleast_nd)
 lazy_xp_function(cov)

tests/test_helpers.py

@@ -24,7 +24,7 @@
 
 from .conftest import np_compat
 
-if TYPE_CHECKING:
+if TYPE_CHECKING:  # pragma: no cover
     # TODO import from typing (requires Python >=3.12)
     from typing_extensions import override
 else: