GH-38768: [Python] Empty slicing an array backwards beyond the start …

…is now empty (#40682) ### What changes are included in this PR? `_normalize_slice` now relies on `slice.indices` (https://docs.python.org/3/reference/datamodel.html#slice.indices). ### Are these changes tested? Yes. ### Are there any user-facing changes? Fixing wrong data returned in an edge case. * GitHub Issue: #40642 * GitHub Issue: #38768 Lead-authored-by: LucasG0 <[email protected]> Co-authored-by: Joris Van den Bossche <[email protected]> Signed-off-by: Joris Van den Bossche <[email protected]>
apache · Apr 9, 2024 · 75a100a · 75a100a
1 parent aeb1618
commit 75a100a
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diff --git a/python/pyarrow/array.pxi b/python/pyarrow/array.pxi
@@ -561,34 +561,7 @@ def _normalize_slice(object arrow_obj, slice key):
         Py_ssize_t start, stop, step
         Py_ssize_t n = len(arrow_obj)
 
-    step = key.step or 1
-
-    if key.start is None:
-        if step < 0:
-            start = n - 1
-        else:
-            start = 0
-    elif key.start < 0:
-        start = key.start + n
-        if start < 0:
-            start = 0
-    elif key.start >= n:
-        start = n
-    else:
-        start = key.start
-
-    if step < 0 and (key.stop is None or key.stop < -n):
-        stop = -1
-    elif key.stop is None:
-        stop = n
-    elif key.stop < 0:
-        stop = key.stop + n
-        if stop < 0:  # step > 0 in this case.
-            stop = 0
-    elif key.stop >= n:
-        stop = n
-    else:
-        stop = key.stop
+    start, stop, step = key.indices(n)
 
     if step != 1:
         indices = np.arange(start, stop, step)

diff --git a/python/pyarrow/tests/test_array.py b/python/pyarrow/tests/test_array.py
@@ -486,6 +486,7 @@ def test_array_slice_negative_step():
         slice(None, None, 2),
         slice(0, 10, 2),
         slice(15, -25, -1),  # GH-38768
+        slice(-22, -22, -1),  # GH-40642
     ]
 
     for case in cases: