BUG/TST: fix test_array_api for cupy

[lucascolley]

Reference issue

N/A

What does this implement/fix?

On main, python dev.py test -t scipy/_lib/tests/test_array_api.py -b cupy gives the following two errors:

================================================================================================= FAILURES =================================================================================================
____________________________________________________________________________________________ test_asarray[cupy] ____________________________________________________________________________________________
scipy/_lib/tests/test_array_api.py:45: in test_asarray
    x, y = as_xparray([0, 1, 2], xp=xp), as_xparray(np.arange(3), xp=xp)
        xp         = <module 'cupy' from '/home/lucas/mambaforge/envs/scipy-dev/lib/python3.11/site-packages/cupy/__init__.py'>
scipy/_lib/_array_api.py:124: in as_xparray
    array = xp.asarray(array, dtype=dtype, copy=copy)
E   TypeError: asarray() got an unexpected keyword argument 'copy'
        array      = [0, 1, 2]
        check_finite = False
        copy       = None
        dtype      = None
        order      = None
        xp         = <module 'cupy' from '/home/lucas/mambaforge/envs/scipy-dev/lib/python3.11/site-packages/cupy/__init__.py'>
_____________________________________________________________________________________________ test_copy[cupy] ______________________________________________________________________________________________
scipy/_lib/tests/test_array_api.py:80: in test_copy
    y = copy(x, xp=_xp)
        _xp        = <module 'cupy' from '/home/lucas/mambaforge/envs/scipy-dev/lib/python3.11/site-packages/cupy/__init__.py'>
        x          = array([1, 2, 3])
        xp         = <module 'cupy' from '/home/lucas/mambaforge/envs/scipy-dev/lib/python3.11/site-packages/cupy/__init__.py'>
scipy/_lib/_array_api.py:165: in copy
    return as_xparray(x, copy=True, xp=xp)
        x          = array([1, 2, 3])
        xp         = <module 'cupy' from '/home/lucas/mambaforge/envs/scipy-dev/lib/python3.11/site-packages/cupy/__init__.py'>
scipy/_lib/_array_api.py:124: in as_xparray
    array = xp.asarray(array, dtype=dtype, copy=copy)
E   TypeError: asarray() got an unexpected keyword argument 'copy'
        array      = array([1, 2, 3])
        check_finite = False
        copy       = True
        dtype      = None
        order      = None
        xp         = <module 'cupy' from '/home/lucas/mambaforge/envs/scipy-dev/lib/python3.11/site-packages/cupy/__init__.py'>
========================================================================================= short test summary info ==========================================================================================
FAILED scipy/_lib/tests/test_array_api.py::test_asarray[cupy] - TypeError: asarray() got an unexpected keyword argument 'copy'
FAILED scipy/_lib/tests/test_array_api.py::test_copy[cupy] - TypeError: asarray() got an unexpected keyword argument 'copy'
======================================================================================= 2 failed, 3 passed in 1.14s ========================================================================================

This is because as_xparray is trying to use the copy parameter of xp.asarray where xp is the 'raw' cupy, which doesn't exist. We should be using the array_api_compat version of cupy instead.

The pattern here, which matches #19051, is that we should only pass namespaces to the xp keyword that are compatible with the standard i.e. after using array_namespace.

For copy, this is relatively obvious: the xp keyword exists for performance reasons, to avoid calling array_namespace twice. The problem with the current test is that it calls array_namespace zero times.

For as_xparray, this is less obvious: it may be that we want it to be able to accept 'raw' namespaces, and fetch the compat version itself. @tupui feel free to change that if wanted, but this PR fixes the issue for now.

---

On this branch, python dev.py test -t scipy/_lib/tests/test_array_api.py -b cupy now passes all tests.

---

Following #19157, this PR also removes the now unnecessary to_numpy (and the test for it), in favour of testing with our new assert_equal rather than np.testing.assert_equal.

Additional information

cc @andyfaff

[tupui]

Thanks @lucascolley. Did you consider moving this logic to as_xparray? I.e, i. Case we provide the namespace, map it to the one that we want instead.

[lucascolley]

Did you consider moving this logic to as_xparray? I.e, i. Case we provide the namespace, map it to the one that we want instead.

We could add that, but is it necessary? I think that we should always be calling array_namespace first, but if you have a concrete example then sounds okay.

[tupui]

To be clear, that would not necessarily change the way we use the API.

To me it just seems that the current parameter xp is not doing what we really want to if we have to massage it a bit. It's going to be error prone as people might forget to do get the namespace before. The alternative would be to make this parameter non optional. Then I think we have a better story.

[lucascolley]

Okay, letting as_xparray take the 'raw' namespace sounds fine. How would you implement this?

[tylerjereddy]

In case Pamphile wants an example shim on as_xparray to criticize, this one seems to have an equivalent effect to the patch in this PR:

--- a/scipy/_lib/_array_api.py
+++ b/scipy/_lib/_array_api.py
@@ -122,7 +122,11 @@ def as_xparray(
         # container that is consistent with the input's namespace.
         array = xp.asarray(array)
     else:
-        array = xp.asarray(array, dtype=dtype, copy=copy)
+        try:
+            array = xp.asarray(array, dtype=dtype, copy=copy)
+        except TypeError:
+            coerced_xp = array_namespace(xp.asarray(3))
+            array = coerced_xp.asarray(array, dtype=dtype, copy=copy)
 
     if check_finite:
         _check_finite(array, xp)
diff --git a/scipy/_lib/tests/test_array_api.py b/scipy/_lib/tests/test_array_api.py
index 1bc393d82..6b2ac1fd4 100644
--- a/scipy/_lib/tests/test_array_api.py
+++ b/scipy/_lib/tests/test_array_api.py
@@ -1,10 +1,9 @@
 import numpy as np
-from numpy.testing import assert_equal
 import pytest
 
 from scipy.conftest import array_api_compatible
 from scipy._lib._array_api import (
-    _GLOBAL_CONFIG, array_namespace, as_xparray, copy
+    _GLOBAL_CONFIG, array_namespace, as_xparray, copy, assert_equal
 )
 
 
@@ -43,7 +42,7 @@ def test_array_namespace():
 @array_api_compatible
 def test_asarray(xp):
     x, y = as_xparray([0, 1, 2], xp=xp), as_xparray(np.arange(3), xp=xp)
-    ref = np.array([0, 1, 2])
+    ref = xp.asarray([0, 1, 2])
     assert_equal(x, ref)
     assert_equal(y, ref)

[lucascolley]

I've resolved the conflicts following gh-19206.

[tupui]

I kind of like what you propose @tylerjereddy. What do you think @lucascolley?

Otherwise this LGTM and we could leave this as a follow up. So approving.

[lucascolley]

Let's go with Tyler's method 👍 I'll modify today

[lucascolley]

@tupui @tylerjereddy all good?

[tylerjereddy]

I did a final confirmation of the testing status improvement locally, then merged, thanks.