BUG: Correct length_of_indexer for range objects (#63872)

Co-authored-by: Richard Shadrach <45562402+rhshadrach@users.noreply.github.com>

Author: vkverma9534

pandas/core/indexers/utils.py

@@ -325,7 +325,18 @@ def length_of_indexer(indexer, target=None) -> int:
             return indexer.sum()
         return len(indexer)
     elif isinstance(indexer, range):
-        return (indexer.stop - indexer.start) // indexer.step
+        try:
+            return len(indexer)
+        except OverflowError:
+            step = indexer.step
+            if step > 0:
+                low, high = indexer.start, indexer.stop
+            else:
+                low, high = indexer.stop, indexer.start
+                step = -step
+            if low >= high:
+                return 0
+            return (high - low - 1) // step + 1
     elif not is_list_like_indexer(indexer):
         return 1
     raise AssertionError("cannot find the length of the indexer")

pandas/tests/indexing/test_indexers.py

@@ -16,6 +16,20 @@ def test_length_of_indexer():
     assert result == 1
 
 
+@pytest.mark.parametrize(
+    "start, stop, step, expected",
+    [
+        (10, 0, -3, 4),
+        (0, 1, 5, 1),
+    ],
+)
+def test_length_of_indexer_range_overflow(start, stop, step, expected):
+    # https://github.com/pandas-dev/pandas/pull/63872
+    indexer = range(start, stop, step)
+    result = length_of_indexer(indexer)
+    assert result == expected
+
+
 def test_is_scalar_indexer():
     indexer = (0, 1)
     assert is_scalar_indexer(indexer, 2)