also use for RangeIndex

Author: topper-123

pandas/core/indexes/base.py

@@ -5180,7 +5180,7 @@ def _getitem_slice(self: _IndexT, slobj: slice) -> _IndexT:
         """
         res = self._data[slobj]
         result = type(self)._simple_new(res, name=self._name)
-        if isinstance(result._engine, libindex.IndexEngine):  # may also be IntervalTree
+        if "_engine" in self._cache:
             reverse = slobj.step is not None and slobj.step < 0
             result._engine._update_from_sliced(self._engine, reverse=reverse)
 

pandas/core/indexes/interval.py

@@ -374,6 +374,13 @@ def __contains__(self, key: Any) -> bool:
         except KeyError:
             return False
 
+    def _getitem_slice(self, slobj: slice) -> IntervalIndex:
+        """
+        Fastpath for __getitem__ when we know we have a slice.
+        """
+        res = self._data[slobj]
+        return type(self)._simple_new(res, name=self._name)
+
     @cache_readonly
     def _multiindex(self) -> MultiIndex:
         return MultiIndex.from_arrays([self.left, self.right], names=["left", "right"])

pandas/core/indexes/range.py

@@ -903,8 +903,7 @@ def __getitem__(self, key):
         Conserve RangeIndex type for scalar and slice keys.
         """
         if isinstance(key, slice):
-            new_range = self._range[key]
-            return self._simple_new(new_range, name=self._name)
+            return self._getitem_slice(key)
         elif is_integer(key):
             new_key = int(key)
             try:
@@ -927,7 +926,12 @@ def _getitem_slice(self: RangeIndex, slobj: slice) -> RangeIndex:
         Fastpath for __getitem__ when we know we have a slice.
         """
         res = self._range[slobj]
-        return type(self)._simple_new(res, name=self._name)
+        result = type(self)._simple_new(res, name=self._name)
+        if "_engine" in self._cache:
+            reverse = slobj.step is not None and slobj.step < 0
+            result._engine._update_from_sliced(self._engine, reverse=reverse)
+
+        return result
 
     @unpack_zerodim_and_defer("__floordiv__")
     def __floordiv__(self, other):