REF: dispatch Series.__setitem__ to loc/iloc, remove redundant helpers

pandas/core/indexing.py

@@ -616,6 +616,8 @@ def _get_setitem_indexer(self, key):
             # invalid indexer type vs 'other' indexing errors
             if "cannot do" in str(e):
                 raise
+            elif "unhashable type" in str(e):
+                raise
             raise IndexingError(key) from e
 
     def _ensure_listlike_indexer(self, key, axis=None):

pandas/core/series.py

@@ -1031,7 +1031,7 @@ def __setitem__(self, key, value):
                 try:
                     self._where(~key, value, inplace=True)
                 except InvalidIndexError:
-                    self._set_values(key.astype(np.bool_), value)
+                    self.iloc[key] = value
                 return
 
             else:
@@ -1049,8 +1049,10 @@ def _set_with_engine(self, key, value):
     def _set_with(self, key, value):
         # other: fancy integer or otherwise
         if isinstance(key, slice):
+            # extract_array so that if we set e.g. ser[-5:] = ser[:5]
+            #  we get the first five values, and not 5 NaNs
             indexer = self.index._convert_slice_indexer(key, kind="getitem")
-            return self._set_values(indexer, value)
+            self.iloc[indexer] = extract_array(value, extract_numpy=True)
 
         else:
             assert not isinstance(key, tuple)
@@ -1068,25 +1070,11 @@ def _set_with(self, key, value):
             #  should be caught by the is_bool_indexer check in __setitem__
             if key_type == "integer":
                 if not self.index._should_fallback_to_positional():
-                    self._set_labels(key, value)
+                    self.loc[key] = value
                 else:
-                    self._set_values(key, value)
+                    self.iloc[key] = value
             else:
-                self._set_labels(key, value)
-
-    def _set_labels(self, key, value):
-        key = com.asarray_tuplesafe(key)
-        indexer: np.ndarray = self.index.get_indexer(key)
-        mask = indexer == -1
-        if mask.any():
-            raise ValueError(f"{key[mask]} not contained in the index")
-        self._set_values(indexer, value)
-
-    def _set_values(self, key, value):
-        if isinstance(key, Series):
-            key = key._values
-        self._mgr = self._mgr.setitem(indexer=key, value=value)
-        self._maybe_update_cacher()
+                self.loc[key] = value
 
     def _set_value(self, label, value, takeable: bool = False):
         """

pandas/tests/series/indexing/test_loc.py

@@ -131,8 +131,8 @@ def test_basic_setitem_with_labels(datetime_series):
 
     inds_notfound = [0, 4, 5, 6]
     arr_inds_notfound = np.array([0, 4, 5, 6])
-    msg = r"\[5\] not contained in the index"
-    with pytest.raises(ValueError, match=msg):
+    msg = r"\[5\] not in index"
+    with pytest.raises(KeyError, match=msg):
         s[inds_notfound] = 0
     with pytest.raises(Exception, match=msg):
         s[arr_inds_notfound] = 0