PERF: RangeIndex.insert maintains RangeIndex when empty (pandas-dev#57833)

Author: mroeschke

doc/source/whatsnew/v3.0.0.rst

@@ -277,6 +277,7 @@ Performance improvements
 - Performance improvement in :meth:`RangeIndex.__getitem__` with a boolean mask or integers returning a :class:`RangeIndex` instead of a :class:`Index` when possible. (:issue:`57588`)
 - Performance improvement in :meth:`RangeIndex.append` when appending the same index (:issue:`57252`)
 - Performance improvement in :meth:`RangeIndex.argmin` and :meth:`RangeIndex.argmax` (:issue:`57823`)
+- Performance improvement in :meth:`RangeIndex.insert` returning a :class:`RangeIndex` instead of a :class:`Index` when the :class:`RangeIndex` is empty. (:issue:`57833`)
 - Performance improvement in :meth:`RangeIndex.round` returning a :class:`RangeIndex` instead of a :class:`Index` when possible. (:issue:`57824`)
 - Performance improvement in :meth:`RangeIndex.join` returning a :class:`RangeIndex` instead of a :class:`Index` when possible. (:issue:`57651`, :issue:`57752`)
 - Performance improvement in :meth:`RangeIndex.reindex` returning a :class:`RangeIndex` instead of a :class:`Index` when possible. (:issue:`57647`, :issue:`57752`)

pandas/core/indexes/range.py

@@ -396,7 +396,7 @@ def __contains__(self, key: Any) -> bool:
         hash(key)
         try:
             key = ensure_python_int(key)
-        except TypeError:
+        except (TypeError, OverflowError):
             return False
         return key in self._range
 
@@ -1009,23 +1009,27 @@ def delete(self, loc) -> Index:  # type: ignore[override]
         return super().delete(loc)
 
     def insert(self, loc: int, item) -> Index:
-        if len(self) and (is_integer(item) or is_float(item)):
+        if is_integer(item) or is_float(item):
             # We can retain RangeIndex is inserting at the beginning or end,
             #  or right in the middle.
-            rng = self._range
-            if loc == 0 and item == self[0] - self.step:
-                new_rng = range(rng.start - rng.step, rng.stop, rng.step)
-                return type(self)._simple_new(new_rng, name=self._name)
-
-            elif loc == len(self) and item == self[-1] + self.step:
-                new_rng = range(rng.start, rng.stop + rng.step, rng.step)
-                return type(self)._simple_new(new_rng, name=self._name)
-
-            elif len(self) == 2 and item == self[0] + self.step / 2:
-                # e.g. inserting 1 into [0, 2]
-                step = int(self.step / 2)
-                new_rng = range(self.start, self.stop, step)
+            if len(self) == 0 and loc == 0 and is_integer(item):
+                new_rng = range(item, item + self.step, self.step)
                 return type(self)._simple_new(new_rng, name=self._name)
+            elif len(self):
+                rng = self._range
+                if loc == 0 and item == self[0] - self.step:
+                    new_rng = range(rng.start - rng.step, rng.stop, rng.step)
+                    return type(self)._simple_new(new_rng, name=self._name)
+
+                elif loc == len(self) and item == self[-1] + self.step:
+                    new_rng = range(rng.start, rng.stop + rng.step, rng.step)
+                    return type(self)._simple_new(new_rng, name=self._name)
+
+                elif len(self) == 2 and item == self[0] + self.step / 2:
+                    # e.g. inserting 1 into [0, 2]
+                    step = int(self.step / 2)
+                    new_rng = range(self.start, self.stop, step)
+                    return type(self)._simple_new(new_rng, name=self._name)
 
         return super().insert(loc, item)
 

pandas/tests/indexes/ranges/test_range.py

@@ -659,6 +659,13 @@ def test_reindex_empty_returns_rangeindex():
     tm.assert_numpy_array_equal(result_indexer, expected_indexer)
 
 
+def test_insert_empty_0_loc():
+    ri = RangeIndex(0, step=10, name="foo")
+    result = ri.insert(0, 5)
+    expected = RangeIndex(5, 15, 10, name="foo")
+    tm.assert_index_equal(result, expected, exact=True)
+
+
 def test_append_non_rangeindex_return_rangeindex():
     ri = RangeIndex(1)
     result = ri.append(Index([1]))