ENH: constants: add array api support (#20593)

Co-authored-by: Ralf Gommers <ralf.gommers@gmail.com>

.github/workflows/array_api.yml

@@ -91,6 +91,7 @@ jobs:
         export OMP_NUM_THREADS=2
         # expand as new modules are added
         python dev.py --no-build test -b all -s cluster -- --durations 3 --timeout=60
+        python dev.py --no-build test -b all -s constants -- --durations 3 --timeout=60
         python dev.py --no-build test -b all -s fft -- --durations 3 --timeout=60
         python dev.py --no-build test -b all -t scipy.special.tests.test_support_alternative_backends -- --durations 3 --timeout=60
         python dev.py --no-build test -b all -t scipy._lib.tests.test_array_api

doc/source/dev/api-dev/array_api.rst

@@ -95,6 +95,7 @@ variable is set:
 
 - `scipy.cluster.hierarchy`
 - `scipy.cluster.vq`
+- `scipy.constants`
 - `scipy.fft`
 
 Support is provided in `scipy.special` for the following functions:

scipy/_lib/_array_api.py

@@ -120,9 +120,11 @@ def array_namespace(*arrays):
 
 
 def _asarray(
-    array, dtype=None, order=None, copy=None, *, xp=None, check_finite=False
+    array, dtype=None, order=None, copy=None, *, xp=None, check_finite=False,
+    subok=False
 ):
-    """SciPy-specific replacement for `np.asarray` with `order` and `check_finite`.
+    """SciPy-specific replacement for `np.asarray` with `order`, `check_finite`, and
+    `subok`.
 
     Memory layout parameter `order` is not exposed in the Array API standard.
     `order` is only enforced if the input array implementation
@@ -131,13 +133,18 @@ def _asarray(
     `check_finite` is also not a keyword in the array API standard; included
     here for convenience rather than that having to be a separate function
     call inside SciPy functions.
+    
+    `subok` is included to allow this function to preserve the behaviour of
+    `np.asanyarray` for NumPy based inputs.
     """
     if xp is None:
         xp = array_namespace(array)
     if xp.__name__ in {"numpy", "scipy._lib.array_api_compat.numpy"}:
         # Use NumPy API to support order
         if copy is True:
-            array = np.array(array, order=order, dtype=dtype)
+            array = np.array(array, order=order, dtype=dtype, subok=subok)
+        elif subok:
+            array = np.asanyarray(array, order=order, dtype=dtype)
         else:
             array = np.asarray(array, order=order, dtype=dtype)
 

scipy/constants/_constants.py

@@ -13,11 +13,13 @@
 from typing import TYPE_CHECKING, Any
 
 from ._codata import value as _cd
-import numpy as np
 
 if TYPE_CHECKING:
     import numpy.typing as npt
 
+from scipy._lib._array_api import array_namespace, _asarray
+
+
 """
 BasSw 2006
 physical constants: imported from CODATA
@@ -269,19 +271,21 @@ def convert_temperature(
     array([ 233.15,  313.15])
 
     """
+    xp = array_namespace(val)
+    _val = _asarray(val, xp=xp, subok=True)
     # Convert from `old_scale` to Kelvin
     if old_scale.lower() in ['celsius', 'c']:
-        tempo = np.asanyarray(val) + zero_Celsius
+        tempo = _val + zero_Celsius
     elif old_scale.lower() in ['kelvin', 'k']:
-        tempo = np.asanyarray(val)
+        tempo = _val
     elif old_scale.lower() in ['fahrenheit', 'f']:
-        tempo = (np.asanyarray(val) - 32) * 5 / 9 + zero_Celsius
+        tempo = (_val - 32) * 5 / 9 + zero_Celsius
     elif old_scale.lower() in ['rankine', 'r']:
-        tempo = np.asanyarray(val) * 5 / 9
+        tempo = _val * 5 / 9
     else:
-        raise NotImplementedError("%s scale is unsupported: supported scales "
-                                  "are Celsius, Kelvin, Fahrenheit, and "
-                                  "Rankine" % old_scale)
+        raise NotImplementedError(f"{old_scale=} is unsupported: supported scales "
+                                   "are Celsius, Kelvin, Fahrenheit, and "
+                                   "Rankine")
     # and from Kelvin to `new_scale`.
     if new_scale.lower() in ['celsius', 'c']:
         res = tempo - zero_Celsius
@@ -292,9 +296,9 @@ def convert_temperature(
     elif new_scale.lower() in ['rankine', 'r']:
         res = tempo * 9 / 5
     else:
-        raise NotImplementedError("'%s' scale is unsupported: supported "
-                                  "scales are 'Celsius', 'Kelvin', "
-                                  "'Fahrenheit', and 'Rankine'" % new_scale)
+        raise NotImplementedError(f"{new_scale=} is unsupported: supported "
+                                   "scales are 'Celsius', 'Kelvin', "
+                                   "'Fahrenheit', and 'Rankine'")
 
     return res
 
@@ -329,7 +333,8 @@ def lambda2nu(lambda_: npt.ArrayLike) -> Any:
     array([  2.99792458e+08,   1.00000000e+00])
 
     """
-    return c / np.asanyarray(lambda_)
+    xp = array_namespace(lambda_)
+    return c / _asarray(lambda_, xp=xp, subok=True)
 
 
 def nu2lambda(nu: npt.ArrayLike) -> Any:
@@ -359,4 +364,5 @@ def nu2lambda(nu: npt.ArrayLike) -> Any:
     array([  2.99792458e+08,   1.00000000e+00])
 
     """
-    return c / np.asanyarray(nu)
+    xp = array_namespace(nu)
+    return c / _asarray(nu, xp=xp, subok=True)

scipy/constants/tests/test_constants.py

@@ -1,35 +1,89 @@
-from numpy.testing import assert_equal, assert_allclose
+import pytest
+
 import scipy.constants as sc
+from scipy.conftest import array_api_compatible
+from scipy._lib._array_api import xp_assert_equal, xp_assert_close
+
+
+pytestmark = [array_api_compatible, pytest.mark.usefixtures("skip_xp_backends")]
+skip_xp_backends = pytest.mark.skip_xp_backends
+
+
+class TestConvertTemperature:
+    def test_convert_temperature(self, xp):
+        xp_assert_equal(sc.convert_temperature(xp.asarray(32.), 'f', 'Celsius'),
+                        xp.asarray(0.0))
+        xp_assert_equal(sc.convert_temperature(xp.asarray([0., 0.]),
+                                               'celsius', 'Kelvin'),
+                        xp.asarray([273.15, 273.15]))
+        xp_assert_equal(sc.convert_temperature(xp.asarray([0., 0.]), 'kelvin', 'c'),
+                        xp.asarray([-273.15, -273.15]))
+        xp_assert_equal(sc.convert_temperature(xp.asarray([32., 32.]), 'f', 'k'),
+                        xp.asarray([273.15, 273.15]))
+        xp_assert_equal(sc.convert_temperature(xp.asarray([273.15, 273.15]),
+                                               'kelvin', 'F'),
+                        xp.asarray([32., 32.]))
+        xp_assert_equal(sc.convert_temperature(xp.asarray([0., 0.]), 'C', 'fahrenheit'),
+                        xp.asarray([32., 32.]))
+        xp_assert_close(sc.convert_temperature(xp.asarray([0., 0.], dtype=xp.float64),
+                                               'c', 'r'),
+                        xp.asarray([491.67, 491.67], dtype=xp.float64),
+                        rtol=0., atol=1e-13)
+        xp_assert_close(sc.convert_temperature(xp.asarray([491.67, 491.67],
+                                                        dtype=xp.float64),
+                                               'Rankine', 'C'),
+                        xp.asarray([0., 0.], dtype=xp.float64), rtol=0., atol=1e-13)
+        xp_assert_close(sc.convert_temperature(xp.asarray([491.67, 491.67],
+                                                        dtype=xp.float64),
+                                               'r', 'F'),
+                        xp.asarray([32., 32.], dtype=xp.float64), rtol=0., atol=1e-13)
+        xp_assert_close(sc.convert_temperature(xp.asarray([32., 32.], dtype=xp.float64),
+                                               'fahrenheit', 'R'),
+                        xp.asarray([491.67, 491.67], dtype=xp.float64),
+                        rtol=0., atol=1e-13)
+        xp_assert_close(sc.convert_temperature(xp.asarray([273.15, 273.15],
+                                                        dtype=xp.float64),
+                                               'K', 'R'),
+                        xp.asarray([491.67, 491.67], dtype=xp.float64),
+                        rtol=0., atol=1e-13)
+        xp_assert_close(sc.convert_temperature(xp.asarray([491.67, 0.],
+                                                          dtype=xp.float64),
+                                               'rankine', 'kelvin'),
+                        xp.asarray([273.15, 0.], dtype=xp.float64), rtol=0., atol=1e-13)
+
+    @skip_xp_backends(np_only=True, reasons=['Python list input uses NumPy backend'])
+    def test_convert_temperature_array_like(self):
+        xp_assert_close(sc.convert_temperature([491.67, 0.], 'rankine', 'kelvin'),
+                        [273.15, 0.], rtol=0., atol=1e-13)
+
+
+    @skip_xp_backends(np_only=True, reasons=['Python int input uses NumPy backend'])
+    def test_convert_temperature_errors(self, xp):
+        with pytest.raises(NotImplementedError, match="old_scale="):
+            sc.convert_temperature(1, old_scale="cheddar", new_scale="kelvin")
+        with pytest.raises(NotImplementedError, match="new_scale="):
+            sc.convert_temperature(1, old_scale="kelvin", new_scale="brie")
+
+
+class TestLambdaToNu:
+    def test_lambda_to_nu(self, xp):
+        xp_assert_equal(sc.lambda2nu(xp.asarray([sc.speed_of_light, 1])),
+                        xp.asarray([1, sc.speed_of_light]))
+
+
+    @skip_xp_backends(np_only=True, reasons=['Python list input uses NumPy backend'])
+    def test_lambda_to_nu_array_like(self, xp):
+        xp_assert_equal(sc.lambda2nu([sc.speed_of_light, 1]),
+                        [1, sc.speed_of_light])
+
 
+class TestNuToLambda:
+    def test_nu_to_lambda(self, xp):
+        xp_assert_equal(sc.nu2lambda(xp.asarray([sc.speed_of_light, 1])),
+                        xp.asarray([1, sc.speed_of_light]))
 
-def test_convert_temperature():
-    assert_equal(sc.convert_temperature(32, 'f', 'Celsius'), 0)
-    assert_equal(sc.convert_temperature([0, 0], 'celsius', 'Kelvin'),
-                 [273.15, 273.15])
-    assert_equal(sc.convert_temperature([0, 0], 'kelvin', 'c'),
-                 [-273.15, -273.15])
-    assert_equal(sc.convert_temperature([32, 32], 'f', 'k'), [273.15, 273.15])
-    assert_equal(sc.convert_temperature([273.15, 273.15], 'kelvin', 'F'),
-                 [32, 32])
-    assert_equal(sc.convert_temperature([0, 0], 'C', 'fahrenheit'), [32, 32])
-    assert_allclose(sc.convert_temperature([0, 0], 'c', 'r'), [491.67, 491.67],
-                    rtol=0., atol=1e-13)
-    assert_allclose(sc.convert_temperature([491.67, 491.67], 'Rankine', 'C'),
-                    [0., 0.], rtol=0., atol=1e-13)
-    assert_allclose(sc.convert_temperature([491.67, 491.67], 'r', 'F'),
-                    [32., 32.], rtol=0., atol=1e-13)
-    assert_allclose(sc.convert_temperature([32, 32], 'fahrenheit', 'R'),
-                    [491.67, 491.67], rtol=0., atol=1e-13)
-    assert_allclose(sc.convert_temperature([273.15, 273.15], 'K', 'R'),
-                    [491.67, 491.67], rtol=0., atol=1e-13)
-    assert_allclose(sc.convert_temperature([491.67, 0.], 'rankine', 'kelvin'),
-                    [273.15, 0.], rtol=0., atol=1e-13)
-
-
-def test_lambda_to_nu():
-    assert_equal(sc.lambda2nu([sc.speed_of_light, 1]), [1, sc.speed_of_light])
-
-
-def test_nu_to_lambda():
-    assert_equal(sc.nu2lambda([sc.speed_of_light, 1]), [1, sc.speed_of_light])
+    @skip_xp_backends(np_only=True, reasons=['Python list input uses NumPy backend'])
+    def test_nu_to_lambda_array_like(self, xp):
+        xp_assert_equal(sc.nu2lambda([sc.speed_of_light, 1]),
+                        [1, sc.speed_of_light])