Fix off-by-one in copy-range

Only when copying a zero-length range can we afford to return the target column. Closes rapidsai#12073.
wence- · Nov 4, 2022 · a3ae461 · a3ae461
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commit a3ae461
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diff --git a/python/cudf/cudf/_lib/copying.pyx b/python/cudf/cudf/_lib/copying.pyx
@@ -144,7 +144,7 @@ def copy_range(Column input_column,
     target_column from target_begin to target_end
     """
 
-    if abs(target_end - target_begin) <= 1:
+    if abs(target_end - target_begin) < 1:
         return target_column
 
     if target_begin < 0:

diff --git a/python/cudf/cudf/tests/test_setitem.py b/python/cudf/cudf/tests/test_setitem.py
@@ -108,6 +108,12 @@ def test_series_set_item(psr, arg):
     assert_eq(psr, gsr)
 
 
+def test_series_setitem_singleton_range():
+    sr = cudf.Series([1, 2, 3], dtype=np.int64)
+    sr.iloc[:1] = np.asarray([7], dtype=np.int64)
+    assert_eq(sr, cudf.Series([7, 2, 3], dtype=np.int64))
+
+
 @pytest.mark.parametrize(
     "df",
     [