Re-introduce __array__ with a warning

Author: asmeurer

array_api_strict/_array_object.py

@@ -17,6 +17,7 @@
 
 import operator
 from enum import IntEnum
+import warnings
 
 from ._creation_functions import asarray
 from ._dtypes import (
@@ -159,23 +160,28 @@ def __repr__(self: Array, /) -> str:
     def __array__(self, dtype: None | np.dtype[Any] = None, copy: None | bool = None) -> npt.NDArray[Any]:
         # We have to allow this to be internally enabled as there's no other
         # easy way to parse a list of Array objects in asarray().
-        if _allow_array:
-            if self._device != CPU_DEVICE:
-                raise RuntimeError(f"Can not convert array on the '{self._device}' device to a Numpy array.")
-            # copy keyword is new in 2.0.0; for older versions don't use it
-            # retry without that keyword.
-            if np.__version__[0] < '2':
-                return np.asarray(self._array, dtype=dtype)
-            elif np.__version__.startswith('2.0.0-dev0'):
-                # Handle dev version for which we can't know based on version
-                # number whether or not the copy keyword is supported.
-                try:
-                    return np.asarray(self._array, dtype=dtype, copy=copy)
-                except TypeError:
-                    return np.asarray(self._array, dtype=dtype)
-            else:
+        if not _allow_array:
+            warnings.warn("The array_api_strict __array__ method was used. "
+            "This method is not part of the array API standard and will be "
+            "removed in a future version of array-api-strict. "
+            "See https://github.com/data-apis/array-api-strict/issues/67 "
+            "for more info.", FutureWarning, stacklevel=2)
+
+        if self._device != CPU_DEVICE:
+            raise RuntimeError(f"Can not convert array on the '{self._device}' device to a Numpy array.")
+        # copy keyword is new in 2.0.0; for older versions don't use it
+        # retry without that keyword.
+        if np.__version__[0] < '2':
+            return np.asarray(self._array, dtype=dtype)
+        elif np.__version__.startswith('2.0.0-dev0'):
+            # Handle dev version for which we can't know based on version
+            # number whether or not the copy keyword is supported.
+            try:
                 return np.asarray(self._array, dtype=dtype, copy=copy)
-        raise ValueError("Conversion from an array_api_strict array to a NumPy ndarray is not supported")
+            except TypeError:
+                return np.asarray(self._array, dtype=dtype)
+        else:
+            return np.asarray(self._array, dtype=dtype, copy=copy)
 
     # These are various helper functions to make the array behavior match the
     # spec in places where it either deviates from or is more strict than

array_api_strict/tests/test_array_object.py

@@ -364,6 +364,11 @@ def test_array_conversion():
         with pytest.raises(RuntimeError, match="Can not convert array"):
             asarray([a])
 
+def test__array__warning():
+    a = ones((2, 3))
+    with pytest.warns(FutureWarning):
+        np.array(a)
+
 def test_allow_newaxis():
     a = ones(5)
     indexed_a = a[None, :]