INT: Use Index._getitem_slice in ArrayManager (#40369)

Author: jorisvandenbossche

pandas/core/internals/array_manager.py

@@ -786,12 +786,10 @@ def get_slice(self, slobj: slice, axis: int = 0) -> ArrayManager:
             arrays = self.arrays[slobj]
 
         new_axes = list(self._axes)
-        new_axes[axis] = new_axes[axis][slobj]
+        new_axes[axis] = new_axes[axis]._getitem_slice(slobj)
 
         return type(self)(arrays, new_axes, verify_integrity=False)
 
-    getitem_mgr = get_slice
-
     def fast_xs(self, loc: int) -> ArrayLike:
         """
         Return the array corresponding to `frame.iloc[loc]`.
@@ -1218,7 +1216,12 @@ def get_slice(self, slobj: slice, axis: int = 0) -> SingleArrayManager:
             raise IndexError("Requested axis not found in manager")
 
         new_array = self.array[slobj]
-        new_index = self.index[slobj]
+        new_index = self.index._getitem_slice(slobj)
+        return type(self)([new_array], [new_index], verify_integrity=False)
+
+    def getitem_mgr(self, indexer) -> SingleArrayManager:
+        new_array = self.array[indexer]
+        new_index = self.index[indexer]
         return type(self)([new_array], [new_index])
 
     def apply(self, func, **kwargs):