From 5385bc89f316f91f83d7a7b461eed68a5507891c Mon Sep 17 00:00:00 2001
From: LucasG0 <guillermou.lucas@gmail.com>
Date: Wed, 20 Mar 2024 00:52:38 +0100
Subject: [PATCH 1/2] Fix empy slicing an array backwards by relying on
 slice.indices

---
 python/pyarrow/array.pxi           | 38 +++---------------------------
 python/pyarrow/tests/test_array.py |  1 +
 2 files changed, 4 insertions(+), 35 deletions(-)

diff --git a/python/pyarrow/array.pxi b/python/pyarrow/array.pxi
index 59d2e91ef6c70..131a9e2b993c3 100644
--- a/python/pyarrow/array.pxi
+++ b/python/pyarrow/array.pxi
@@ -561,41 +561,9 @@ 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
-
-    if step != 1:
-        indices = np.arange(start, stop, step)
-        return arrow_obj.take(indices)
-    else:
-        length = max(stop - start, 0)
-        return arrow_obj.slice(start, length)
+    start, stop, step = key.indices(n)
+    indices = np.arange(start, stop, step)
+    return arrow_obj.take(indices)
 
 
 cdef Py_ssize_t _normalize_index(Py_ssize_t index,
diff --git a/python/pyarrow/tests/test_array.py b/python/pyarrow/tests/test_array.py
index 60794ebef3281..472a6c5dce750 100644
--- 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:

From b9df1e60a3b5704d22072e58dab2c476cdffad8e Mon Sep 17 00:00:00 2001
From: LucasG0 <guillermou.lucas@gmail.com>
Date: Mon, 25 Mar 2024 01:04:41 +0100
Subject: [PATCH 2/2] Use zero-copy slice when step=1

---
 python/pyarrow/array.pxi | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/python/pyarrow/array.pxi b/python/pyarrow/array.pxi
index 131a9e2b993c3..45fd29ad3b3f3 100644
--- a/python/pyarrow/array.pxi
+++ b/python/pyarrow/array.pxi
@@ -562,8 +562,13 @@ def _normalize_slice(object arrow_obj, slice key):
         Py_ssize_t n = len(arrow_obj)
 
     start, stop, step = key.indices(n)
-    indices = np.arange(start, stop, step)
-    return arrow_obj.take(indices)
+
+    if step != 1:
+        indices = np.arange(start, stop, step)
+        return arrow_obj.take(indices)
+    else:
+        length = max(stop - start, 0)
+        return arrow_obj.slice(start, length)
 
 
 cdef Py_ssize_t _normalize_index(Py_ssize_t index,