Unit tests WIP

array_api_compat/common/_helpers.py

@@ -804,17 +804,26 @@ def size(x):
     return math.prod(x.shape)
 
 
-def is_writeable_array(x):
+def is_writeable_array(x) -> bool:
     """
     Return False if x.__setitem__ is expected to raise; True otherwise
     """
     if is_numpy_array(x):
         return x.flags.writeable
-    if is_jax_array(x):
+    if is_jax_array(x) or is_pydata_sparse_array(x):
         return False
     return True
 
 
+def _is_fancy_index(idx) -> bool:
+    if not isinstance(idx, tuple):
+        idx = (idx,)
+    return any(
+        isinstance(i, (list, tuple)) or is_array_api_obj(i)
+        for i in idx
+    )
+
+
 _undef = object()
 
 
@@ -900,7 +909,7 @@ def __getitem__(self, idx):
         and feels more intuitive coming from the JAX documentation.
         """
         if self.idx is not _undef:
-            raise TypeError("Index has already been set")
+            raise ValueError("Index has already been set")
         self.idx = idx
         return self
 
@@ -911,14 +920,12 @@ def _common(
         copy: bool | None | Literal["_force_false"] = True,
         **kwargs,
     ):
-        """Validate kwargs and perform common prepocessing.
+        """Perform common prepocessing.
 
         Returns
         -------
-        If the operation can be resolved by at[],
-            (return value, None)
-        Otherwise,
-            (None, preprocessed x)
+        If the operation can be resolved by at[], (return value, None)
+        Otherwise, (None, preprocessed x)
         """
         if self.idx is _undef:
             raise TypeError(
@@ -929,40 +936,44 @@ def _common(
                 "    at(x)[idx].set(value)\n"
                 "(same for all other methods)."
             )
+
+        x = self.x
 
         if copy is False:
-            if not is_writeable_array(self.x):
-                raise ValueError("Cannot avoid modifying parameter in place")
+            if not is_writeable_array(x) or is_dask_array(x):
+                raise ValueError("Cannot modify parameter in place")
         elif copy is None:
-            copy = not is_writeable_array(self.x)
+            copy = not is_writeable_array(x)
         elif copy == "_force_false":
             copy = False
         elif copy is not True:
             raise ValueError(f"Invalid value for copy: {copy!r}")
 
-        if copy and is_jax_array(self.x):
+        if is_jax_array(x):
             # Use JAX's at[]
-            at_ = self.x.at[self.idx]
+            at_ = x.at[self.idx]
             args = (y,) if y is not _undef else ()
             return getattr(at_, at_op)(*args, **kwargs), None
 
         # Emulate at[] behaviour for non-JAX arrays
-        # FIXME We blindly expect the output of x.copy() to be always writeable.
-        # This holds true for read-only numpy arrays, but not necessarily for
-        # other backends.
-        x = self.x.copy() if copy else self.x
+        if copy:
+            # FIXME We blindly expect the output of x.copy() to be always writeable.
+            # This holds true for read-only numpy arrays, but not necessarily for
+            # other backends.
+            xp = get_namespace(x)
+            x = xp.asarray(x, copy=True)
+
         return None, x
 
     def get(self, copy: bool | None = True, **kwargs):
-        """Return x[idx]. In addition to plain __getitem__, this allows ensuring
-        that the output is (not) a copy and kwargs are passed to the backend."""
-        # Special case when xp=numpy and idx is a fancy index
-        # If copy is not False, avoid an unnecessary double copy.
-        # if copy is forced to False, raise.
-        if is_numpy_array(self.x) and (
-            isinstance(self.idx, (list, tuple))
-            or (is_numpy_array(self.idx) and self.idx.dtype.kind in "biu")
-        ):
+        """
+        Return x[idx]. In addition to plain __getitem__, this allows ensuring
+        that the output is (not) a copy and kwargs are passed to the backend.
+        """
+        # __getitem__ with a fancy index always returns a copy.
+        # Avoid an unnecessary double copy.
+        # If copy is forced to False, raise.
+        if _is_fancy_index(self.idx):
             if copy is False:
                 raise ValueError(
                     "Indexing a numpy array with a fancy index always "
@@ -1032,13 +1043,15 @@ def power(self, y, /, **kwargs):
 
     def min(self, y, /, **kwargs):
         """x[idx] = minimum(x[idx], y)"""
-        xp = array_namespace(self.x)
-        return self._iop("min", xp.minimum, y, **kwargs)
+        import numpy as np
+
+        return self._iop("min", np.minimum, y, **kwargs)
 
     def max(self, y, /, **kwargs):
         """x[idx] = maximum(x[idx], y)"""
-        xp = array_namespace(self.x)
-        return self._iop("max", xp.maximum, y, **kwargs)
+        import numpy as np
+
+        return self._iop("max", np.maximum, y, **kwargs)
 
 
 __all__ = [

tests/test_at.py

@@ -0,0 +1,158 @@
+from __future__ import annotations
+
+from contextlib import contextmanager, suppress
+
+import numpy as np
+import pytest
+
+from array_api_compat import (
+    array_namespace,
+    at,
+    is_dask_array,
+    is_jax_array,
+    is_torch_namespace,
+    is_pydata_sparse_array,
+    is_writeable_array,
+)
+from ._helpers import import_, all_libraries
+
+
+def assert_array_equal(a, b):
+    if is_pydata_sparse_array(a):
+        a = a.todense()
+    elif is_dask_array(a):
+        a = a.compute()
+    np.testing.assert_array_equal(a, b)
+
+
+@contextmanager
+def assert_copy(x, copy: bool | None):
+    # dask arrays are writeable, but writing to them will hot-swap the
+    # dask graph inside the collection so that anything that references
+    # the original graph, i.e. the input collection, won't be mutated.
+    if copy is False and (not is_writeable_array(x) or is_dask_array(x)):
+        with pytest.raises((TypeError, ValueError)):
+            yield
+        return
+
+    xp = array_namespace(x)
+    x_orig = xp.asarray(x, copy=True)
+    yield
+
+    if is_dask_array(x):
+        expect_copy = True
+    elif copy is None:
+        expect_copy = not is_writeable_array(x)
+    else:
+        expect_copy = copy
+    assert_array_equal((x == x_orig).all(), expect_copy)
+
+
+@pytest.fixture(params=all_libraries + ["np_readonly"])
+def x(request):
+    library = request.param
+    if library == "np_readonly":
+        x = np.asarray([10, 20, 30])
+        x.flags.writeable = False
+    else:
+        lib = import_(library)
+        x = lib.asarray([10, 20, 30])
+    return x
+
+
+@pytest.mark.parametrize("copy", [True, False, None])
+@pytest.mark.parametrize(
+    "op,arg,expect",
+    [
+        ("apply", np.negative, [10, -20, -30]),
+        ("set", 40, [10, 40, 40]),
+        ("add", 40, [10, 60, 70]),
+        ("subtract", 100, [10, -80, -70]),
+        ("multiply", 2, [10, 40, 60]),
+        ("divide", 3, [10, 6, 10]),
+        ("power", 2, [10, 400, 900]),
+        ("min", 25, [10, 20, 25]),
+        ("max", 25, [10, 25, 30]),
+    ],
+)
+def test_operations(x, copy, op, arg, expect):
+    with assert_copy(x, copy):
+        y = getattr(at(x, slice(1, None)), op)(arg, copy=copy)
+        assert isinstance(y, type(x))
+        assert_array_equal(y, expect)
+
+
+@pytest.mark.parametrize("copy", [True, False, None])
+def test_get(x, copy):
+    with assert_copy(x, copy):
+        y = at(x, slice(2)).get(copy=copy)
+        assert isinstance(y, type(x))
+        assert_array_equal(y, [10, 20])
+        # Let assert_copy test that y is a view or copy
+        with suppress((TypeError, ValueError)):
+            y[0] = 40
+
+
+@pytest.mark.parametrize(
+    "idx",
+    [
+        [0, 1],
+        (0, 1),
+        np.array([0, 1], dtype="i1"),
+        np.array([0, 1], dtype="u1"),
+        lambda xp: xp.asarray([0, 1], dtype="i1"),
+        lambda xp: xp.asarray([0, 1], dtype="u1"),
+        [True, True, False],
+        (True, True, False),
+        np.array([True, True, False]),
+        lambda xp: xp.asarray([True, True, False]),
+    ],
+)
+@pytest.mark.parametrize("tuple_index", [True, False])
+def test_get_fancy_indices(x, idx, tuple_index):
+    """get() with a fancy index always returns a copy"""
+    if callable(idx):
+        xp = array_namespace(x)
+        idx = idx(xp)
+
+    if is_jax_array(x) and isinstance(idx, (list, tuple)):
+        pytest.skip("JAX fancy indices must always be arrays")
+    if is_pydata_sparse_array(x) and is_pydata_sparse_array(idx):
+        pytest.skip("sparse fancy indices can't be sparse themselves")
+    if is_dask_array(x) and isinstance(idx, tuple):
+        pytest.skip("dask does not support tuples; only lists or arrays")
+    if isinstance(idx, tuple) and not tuple_index:
+        pytest.skip("tuple indices must always be wrapped in a tuple")
+
+    if tuple_index:
+        idx = (idx,)
+
+    with assert_copy(x, True):
+        y = at(x, idx).get()
+        assert isinstance(y, type(x))
+        assert_array_equal(y, [10, 20])
+        # Let assert_copy test that y is a view or copy
+        with suppress((TypeError, ValueError)):
+            y[0] = 40
+
+    with assert_copy(x, True):
+        y = at(x, idx).get(copy=None)
+        assert isinstance(y, type(x))
+        assert_array_equal(y, [10, 20])
+        # Let assert_copy test that y is a view or copy
+        with suppress((TypeError, ValueError)):
+            y[0] = 40
+
+    with pytest.raises(ValueError, match="fancy index"):
+        at(x, idx).get(copy=False)
+
+
+def test_variant_index_syntax(x):
+    y = at(x)[:2].set(40)
+    assert isinstance(y, type(x))
+    assert_array_equal(y, [40, 40, 30])
+
+    with pytest.raises(ValueError):
+        at(x, 1)[2]
+    with pytest.raises(ValueError):
+        at(x)[1][2]

tests/test_common.py

@@ -5,7 +5,7 @@
     is_dask_namespace, is_jax_namespace, is_pydata_sparse_namespace,
 )
 
-from array_api_compat import is_array_api_obj, device, to_device
+from array_api_compat import device, is_array_api_obj, is_writeable_array, to_device
 
 from ._helpers import import_, wrapped_libraries, all_libraries
 
@@ -55,6 +55,25 @@ def test_is_xp_namespace(library, func):
     assert is_func(lib) == (func == is_namespace_functions[library])
 
 
+@pytest.mark.parametrize("library", all_libraries)
+def test_is_writeable_array(library):
+    lib = import_(library)
+    x = lib.asarray([1, 2, 3])
+    if is_writeable_array(x):
+        x[1] = 4
+        np.testing.assert_equal(np.asarray(x), [1, 4, 3])
+    else:
+        with pytest.raises((TypeError, ValueError)):
+            x[1] = 4
+
+
+def test_is_writeable_array_numpy():
+    x = np.asarray([1, 2, 3])
+    assert is_writeable_array(x)
+    x.flags.writeable = False
+    assert not is_writeable_array(x)
+
+
 @pytest.mark.parametrize("library", all_libraries)
 def test_device(library):
     xp = import_(library, wrapper=True)