ENH: Add __array__ to the array_api Array object

This is *NOT* part of the array API spec (so it should not be relied on for
portable code). However, without this, np.asarray(np.array_api.Array) produces
an object array instead of doing the conversion to a NumPy array as expected.
This would work once np.asarray() implements dlpack support, but until then,
it seems reasonable to make the conversion work.

Note that the reverse, calling np.array_api.asarray(np.array), already works
because np.array_api.asarray() is just a wrapper for np.asarray().

Original NumPy Commit: 74a3ee7a8b75bf6dc271c9a1a4b55d2ad9758420

Author: asmeurer

array_api_strict/_array_object.py

@@ -108,6 +108,17 @@ def __repr__(self: Array, /) -> str:
             mid = np.array2string(self._array, separator=', ', prefix=prefix, suffix=suffix)
         return prefix + mid + suffix
 
+    # This function is not required by the spec, but we implement it here for
+    # convenience so that np.asarray(np.array_api.Array) will work.
+    def __array__(self, dtype=None):
+        """
+        Warning: this method is NOT part of the array API spec. Implementers
+        of other libraries need not include it, and users should not assume it
+        will be present in other implementations.
+
+        """
+        return np.asarray(self._array, dtype=dtype)
+
     # 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
     # NumPy behavior

array_api_strict/tests/test_array_object.py

@@ -315,3 +315,10 @@ def test_array_properties():
     assert a.mT.shape == (1, 3, 2)
     assert isinstance(b.mT, Array)
     assert b.mT.shape == (3, 2)
+
+def test___array__():
+    a = ones((2, 3), dtype=int16)
+    assert np.asarray(a) is a._array
+    b = np.asarray(a, dtype=np.float64)
+    assert np.all(np.equal(b, np.ones((2, 3), dtype=np.float64)))
+    assert b.dtype == np.float64