utility method to inverse a slice

src/est/core/utils/slicing.py

+def reverse_slice(in_slice: slice) -> slice:
+    """
+    Returns a new slice object that reverses the given slice.
+    Ensures that `data[in_slice][::-1] == data[reverse_slice(in_slice)]`.
+
+    :param in_slice: A slice object.
+    :return: A reversed slice object.
+    """
+    start, stop, step = in_slice.start, in_slice.stop, in_slice.step
+
+    if step is None:
+        step = 1
+
+    if step > 0:
+        start_inv = stop - step if stop is not None else None
+        stop_inv = start - step if start is not None else None
+    else:
+        start_inv = stop + step if stop is not None else None
+        stop_inv = start + step if start is not None else None
+
+    step_inv = -step
+
+    return slice(start_inv, stop_inv, step_inv)

src/est/tests/test_slicing.py

+from numpy.random import RandomState
+
+from est.core.utils.slicing import reverse_slice
+
+
+def test_reverse_slice():
+    rng = RandomState(42)
+    data = list(range(100))
+    for _ in range(1000):
+        start = rng.choice([None] * 20 + list(range(-150, 150)))
+        stop = rng.choice([None] * 20 + list(range(-150, 150)))
+        step = rng.choice([-10, -5, -3, -2, -1, 1, 2, 3, 5, 10, None])
+
+        in_slice = slice(start, stop, step)
+        rev_slice = reverse_slice(in_slice)
+
+        expected = data[in_slice][::-1]
+        actual = data[rev_slice]
+
+        assert expected == actual, f"Failed for slice({start}, {stop}, {step})"