Refactor get/setitem for nonunit steps

src/blosc2/ndarray.py

@@ -3945,20 +3945,12 @@ def get_fselection_numpy(self, key: list | np.ndarray) -> np.ndarray:
         # Default when there are booleans
         # TODO: for boolean indexing could be optimised by avoiding
         # calculating out_shape prior to loop and keeping track on-the-fly (like in LazyExpr machinery)
-        return self._get_set_findex_default(_slice, out_shape)
-
-    def _get_set_findex_default(self, _slice, out_shape=None, updater=None):
-        _get = False
-        if not ((out_shape is None) or (updater is None)):
-            raise ValueError("Cannot provide both out_shape and updater.")
-        # we have a getitem
-        if out_shape is not None:
-            _get = True
-            out = np.empty(out_shape, dtype=self.dtype)
-        elif updater is None:
-            raise ValueError("Must provide one of out_shape or updater.")
-        else:
-            out = self  # default return for no intersecting chunks
+        out = np.empty(out_shape, dtype=self.dtype)
+        return self._get_set_findex_default(_slice, out)
+
+    def _get_set_findex_default(self, _slice, out=None, value=None):
+        _get = out is not None
+        out = self if out is None else out  # default return for setitem with no intersecting chunks
         if 0 in self.shape:
             return out
         chunk_size = ndindex.ChunkSize(self.chunks)  # only works with nonzero chunks
@@ -3973,10 +3965,10 @@ def _get_set_findex_default(self, _slice, out_shape=None, updater=None):
             chunk = np.empty(tuple(sp - st for st, sp in zip(start, stop, strict=True)), dtype=self.dtype)
             super().get_slice_numpy(chunk, (start, stop))
             if _get:
-                new_shape = sel_idx.newshape(out_shape)
+                new_shape = sel_idx.newshape(out.shape)
                 out[sel_idx.raw] = chunk[sub_idx].reshape(new_shape)
             else:
-                chunk[sub_idx] = updater(sel_idx.raw)
+                chunk[sub_idx] = value if np.isscalar(value) else value[sel_idx]
                 out = super().set_slice((start, stop), chunk)
         return out
 
@@ -3998,7 +3990,42 @@ def set_oselection_numpy(self, key: list | np.ndarray, arr: NDArray) -> np.ndarr
         """
         return super().set_oindex_numpy(key, arr)
 
-    def __getitem__(  # noqa: C901
+    def _get_set_nonunit_steps(self, _slice, out=None, value=None):
+        start, stop, step, mask = _slice
+        _get = out is not None
+        out = self if out is None else out  # default return for setitem with no intersecting chunks
+        if 0 in self.shape:
+            return out
+
+        chunks = self.chunks
+        _slice = tuple(slice(s, st, stp) for s, st, stp in zip(start, stop, step, strict=True))
+        intersecting_chunks = [
+            slice_to_chunktuple(s, c) for s, c in zip(_slice, chunks, strict=True)
+        ]  # internally handles negative steps
+        for c in product(*intersecting_chunks):
+            sel_idx, glob_selection, sub_idx = _get_selection(c, _slice, chunks)
+            sel_idx = tuple(s for s, m in zip(sel_idx, mask, strict=True) if not m)
+            sub_idx = tuple(s if not m else s.start for s, m in zip(sub_idx, mask, strict=True))
+            locstart, locstop = _get_local_slice(
+                glob_selection,
+                (),
+                ((), ()),  # switches start and stop for negative steps
+            )
+            chunk = np.empty(
+                tuple(sp - st for st, sp in zip(locstart, locstop, strict=True)), dtype=self.dtype
+            )
+            # basically load whole chunk, except for slice part at beginning and end
+            super().get_slice_numpy(chunk, (locstart, locstop))  # copy relevant slice of chunk
+            if _get:
+                out[sel_idx] = chunk[sub_idx]  # update relevant parts of chunk
+            else:
+                chunk[sub_idx] = (
+                    value if np.isscalar(value) else value[sel_idx]
+                )  # update relevant parts of chunk
+                out = super().set_slice((locstart, locstop), chunk)  # load updated partial chunk into array
+        return out
+
+    def __getitem__(
         self,
         key: None
         | int
@@ -4080,7 +4107,8 @@ def __getitem__(  # noqa: C901
                 if key:
                     _slice = ndindex.ndindex(()).expand(self.shape)  # just get whole array
                     out_shape = _slice.newshape(self.shape)
-                    return np.expand_dims(self._get_set_findex_default(_slice, out_shape=out_shape), 0)
+                    out = np.empty(out_shape, dtype=self.dtype)
+                    return np.expand_dims(self._get_set_findex_default(_slice, out=out), 0)
                 else:  # do nothing
                     return np.empty((0,) + self.shape, dtype=self.dtype)
             elif (
@@ -4096,12 +4124,9 @@ def __getitem__(  # noqa: C901
             return self.get_fselection_numpy(key)  # fancy index default, can be quite slow
 
         start, stop, step, none_mask = get_ndarray_start_stop(self.ndim, key_, self.shape)
-        for i, s in enumerate(step):  # (start, stop, -1) => stop < start
-            if s < 0:
-                temp = start[i]
-                start[i] = stop[i] + 1  # don't want to include stop
-                stop[i] = temp + 1  # want to include start
-        shape = np.array([sp - st for st, sp in zip(start, stop, strict=True)])
+        shape = np.array(
+            [(sp - st - np.sign(stp)) // stp + 1 for st, sp, stp in zip(start, stop, step, strict=True)]
+        )
         if mask is not None:  # there are some dummy dims from ints
             # only get mask for not Nones in key to have nm_ same length as shape
             nm_ = [not m for m, n in zip(mask, none_mask, strict=True) if not n]
@@ -4110,12 +4135,11 @@ def __getitem__(  # noqa: C901
             shape = tuple(shape[nm_])
 
         # Create the array to store the result
-        arr = np.empty(shape, dtype=self.dtype)
-        nparr = super().get_slice_numpy(arr, (start, stop))
-        if step != (1,) * self.ndim:  # TODO: optimise to work like __setitem__ for non-unit steps
-            # have to make step refer to sliced dims (which will be less if ints present)
-            slice_ = tuple(slice(None, None, st) for st, m in zip(step, nm_, strict=True) if m)
-            nparr = nparr[slice_]
+        nparr = np.empty(shape, dtype=self.dtype)
+        if step != (1,) * self.ndim:
+            nparr = self._get_set_nonunit_steps((start, stop, step, [not i for i in nm_]), out=nparr)
+        else:
+            nparr = super().get_slice_numpy(nparr, (start, stop))
 
         if np.any(none_mask):
             nparr = np.expand_dims(nparr, axis=[i for i, n in enumerate(none_mask) if n])
@@ -4127,7 +4151,7 @@ def __getitem__(  # noqa: C901
 
         return nparr
 
-    def __setitem__(  # noqa : C901
+    def __setitem__(
         self,
         key: None | int | slice | Sequence[slice | int | np.bool_ | np.ndarray[int | np.bool_] | None],
         value: object,
@@ -4171,14 +4195,6 @@ def __setitem__(  # noqa : C901
         if hasattr(value, "shape") and value.shape == ():
             value = value.item()
 
-        def updater(sel_idx):
-            return value[sel_idx]
-
-        if np.isscalar(value):  # overwrite updater function for simple cases (faster)
-
-            def updater(sel_idx):
-                return value
-
         if builtins.any(isinstance(k, (list, np.ndarray)) for k in key_):  # fancy indexing
             _slice = ndindex.ndindex(key_).expand(
                 self.shape
@@ -4191,36 +4207,14 @@ def updater(sel_idx):
                     _slice = ndindex.ndindex(()).expand(self.shape)  # just get whole array
                 else:  # do nothing
                     return self
-            return self._get_set_findex_default(_slice, updater=updater)
+            return self._get_set_findex_default(_slice, value=value)
 
         start, stop, step, none_mask = get_ndarray_start_stop(self.ndim, key_, self.shape)
 
         if step != (1,) * self.ndim:  # handle non-unit or negative steps
             if np.any(none_mask):
                 raise ValueError("Cannot mix non-unit steps and None indexing for __setitem__.")
-            chunks = self.chunks
-            shape = self.shape
-            _slice = tuple(slice(s, st, stp) for s, st, stp in zip(start, stop, step, strict=True))
-            intersecting_chunks = [
-                slice_to_chunktuple(s, c) for s, c in zip(_slice, chunks, strict=True)
-            ]  # internally handles negative steps
-            out = self  # for when shape has 0 (i.e. arr is empty, as then skip loop)
-            for c in product(*intersecting_chunks):
-                sel_idx, glob_selection, sub_idx = _get_selection(c, _slice, chunks)
-                sel_idx = tuple(s for s, m in zip(sel_idx, mask, strict=True) if not m)
-                sub_idx = tuple(s if not m else s.start for s, m in zip(sub_idx, mask, strict=True))
-                locstart, locstop = _get_local_slice(
-                    glob_selection,
-                    (),
-                    ((), ()),  # switches start and stop for negative steps
-                )
-                chunk = np.empty(
-                    tuple(sp - st for st, sp in zip(locstart, locstop, strict=True)), dtype=self.dtype
-                )
-                super().get_slice_numpy(chunk, (locstart, locstop))  # copy relevant slice of chunk
-                chunk[sub_idx] = updater(sel_idx)  # update relevant parts of chunk
-                out = super().set_slice((locstart, locstop), chunk)  # load updated partial chunk into array
-            return out
+            return self._get_set_nonunit_steps((start, stop, step, mask), value=value)
 
         shape = [sp - st for sp, st in zip(stop, start, strict=False)]
         if isinstance(value, NDArray):
@@ -6313,7 +6307,7 @@ def _get_selection(ctuple, ptuple, chunks):
     out_pselection = ()
     i = 0
     for ps, pt in zip(pselection, ptuple, strict=True):
-        sign_ = pt.step // builtins.abs(pt.step)
+        sign_ = np.sign(pt.step)
         n = (ps.start - pt.start - sign_) // pt.step
         out_start = n + 1
         # ps.stop always positive except for case where get full array (it is then -1 since desire 0th element)

tests/ndarray/test_getitem.py

@@ -16,6 +16,7 @@
 argvalues = [
     ([456], [258], [73], slice(0, 1), np.int32),
     ([77, 134, 13], [31, 13, 5], [7, 8, 3], (slice(3, 7), slice(50, 100), 7), np.float64),
+    ([77, 134, 13], [31, 13, 5], [7, 8, 3], (slice(3, 56, 3), slice(100, 50, -4), 7), np.float64),
     ([12, 13, 14, 15, 16], [5, 5, 5, 5, 5], [2, 2, 2, 2, 2], (slice(1, 3), ..., slice(3, 6)), np.float32),
 ]