FIX: type-var for idx in Series.loc.__setitem__(...) (#1670)

* Fix type-var for `idx` in `Series.loc.__setitem__(...)`

Fixes #1669 .

* TST: GH1669 Add testing to `Series.loc.__setitem__` when element types don't match

* Fix newly added part in `test_series_loc_setitem` so that it could be runnable

* Change `IndexOpsMixin[Any]` to `IndexOpsMixin`

Co-authored-by: Yi-Fan Wang <cmp0xff@users.noreply.github.com>

---------

Co-authored-by: Yi-Fan Wang <cmp0xff@users.noreply.github.com>

Author: Azureblade3808

pandas-stubs/core/series.pyi

@@ -317,7 +317,7 @@ class _LocIndexerSeries(_LocIndexer, Generic[S1]):
     @overload
     def __setitem__(
         self,
-        idx: IndexOpsMixin[S1] | MaskType | slice,
+        idx: IndexOpsMixin | MaskType | slice,
         value: S1 | ArrayLike | IndexOpsMixin[S1] | None,
     ) -> None: ...
     @overload

tests/series/test_indexing.py

@@ -93,6 +93,12 @@ def test_series_loc_setitem() -> None:
     v = s.loc[[0, 2, 4]].values
     s.loc[[0, 2, 4]] = v
 
+    # GH 1669
+    s = pd.Series([1, 2, 3, 4, 5], index=["a", "b", "c", "d", "e"])
+    idx = pd.Index(["a", "c", "e"])
+    v = s.loc[idx].values
+    s.loc[idx] = v
+
 
 def test_series_isin() -> None:
     s = pd.Series([1, 2, 3, 4, 5])