BUG: astype(..., copy=True) doesn't copy on dask

array_api_compat/dask/array/_aliases.py

@@ -39,7 +39,14 @@
 
 isdtype = get_xp(np)(_aliases.isdtype)
 unstack = get_xp(da)(_aliases.unstack)
-astype = _aliases.astype
+
+def astype(x: Array, dtype: Dtype, /, *, copy: bool = True) -> Array:
+    if not copy and dtype == x.dtype:
+        return x
+    # dask astype doesn't respect copy=True so copy
+    # manually via numpy
+    x = np.array(x, dtype=dtype, copy=copy)
+    return da.from_array(x)
 
 # Common aliases
 

tests/test_common.py

@@ -272,3 +272,16 @@ def test_asarray_copy(library):
         assert all(b[0] == 1.0)
     else:
         assert all(b[0] == 0.0)
+
+@pytest.mark.parametrize("library", wrapped_libraries)
+def test_astype_copy(library):
+    # array-api-tests currently doesn't check copy=True
+    # makes a copy when dtypes are the same
+    # so we check that here
+    xp = import_(library, wrapper=True)
+    a = xp.asarray([1])
+    b = xp.astype(a, a.dtype, copy=True)
+
+    a[0] = 10
+
+    assert b[0] == 1