REF/TYP: stricter typing for Series._slice (#52190)

Author: jbrockmendel

pandas/core/frame.py

@@ -3758,18 +3758,10 @@ def __getitem__(self, key):
 
             elif is_mi and self.columns.is_unique and key in self.columns:
                 return self._getitem_multilevel(key)
+
         # Do we have a slicer (on rows)?
         if isinstance(key, slice):
-            indexer = self.index._convert_slice_indexer(key, kind="getitem")
-            if isinstance(indexer, np.ndarray):
-                # reachable with DatetimeIndex
-                indexer = lib.maybe_indices_to_slice(
-                    indexer.astype(np.intp, copy=False), len(self)
-                )
-                if isinstance(indexer, np.ndarray):
-                    # GH#43223 If we can not convert, use take
-                    return self.take(indexer, axis=0)
-            return self._slice(indexer, axis=0)
+            return self._getitem_slice(key)
 
         # Do we have a (boolean) DataFrame?
         if isinstance(key, DataFrame):

pandas/core/generic.py

@@ -4150,7 +4150,26 @@ class   animal   locomotion
     def __getitem__(self, item):
         raise AbstractMethodError(self)
 
-    def _slice(self, slobj: slice, axis: Axis = 0) -> Self:
+    @final
+    def _getitem_slice(self, key: slice) -> Self:
+        """
+        __getitem__ for the case where the key is a slice object.
+        """
+        # _convert_slice_indexer to determine if this slice is positional
+        #  or label based, and if the latter, convert to positional
+        slobj = self.index._convert_slice_indexer(key, kind="getitem")
+        if isinstance(slobj, np.ndarray):
+            # reachable with DatetimeIndex
+            indexer = lib.maybe_indices_to_slice(
+                slobj.astype(np.intp, copy=False), len(self)
+            )
+            if isinstance(indexer, np.ndarray):
+                # GH#43223 If we can not convert, use take
+                return self.take(indexer, axis=0)
+            slobj = indexer
+        return self._slice(slobj)
+
+    def _slice(self, slobj: slice, axis: AxisInt = 0) -> Self:
         """
         Construct a slice of this container.
 

pandas/core/series.py

@@ -943,10 +943,12 @@ def _ixs(self, i: int, axis: AxisInt = 0) -> Any:
         """
         return self._values[i]
 
-    def _slice(self, slobj: slice | np.ndarray, axis: Axis = 0) -> Series:
+    def _slice(self, slobj: slice, axis: AxisInt = 0) -> Series:
         # axis kwarg is retained for compat with NDFrame method
         #  _slice is *always* positional
-        return self._get_values(slobj)
+        mgr = self._mgr.get_slice(slobj, axis=axis)
+        out = self._constructor(mgr, fastpath=True)
+        return out.__finalize__(self)
 
     def __getitem__(self, key):
         check_dict_or_set_indexers(key)
@@ -983,10 +985,7 @@ def __getitem__(self, key):
 
         if isinstance(key, slice):
             # Do slice check before somewhat-costly is_bool_indexer
-            # _convert_slice_indexer to determine if this slice is positional
-            #  or label based, and if the latter, convert to positional
-            slobj = self.index._convert_slice_indexer(key, kind="getitem")
-            return self._slice(slobj)
+            return self._getitem_slice(key)
 
         if is_iterator(key):
             key = list(key)