Fix issue with Series.loc[x] where x is a tuple specifiying a specific index to get from a MultiIndex (#350)

* WIP: TimedeltaIndex accessors

* remove dtl to make mypy happy

* demonstrate possible bug

* fix series loc on multiindex scalars

* use IndexSliceTuple, add comments

Author: Dr-Irv

pandas-stubs/core/series.pyi

@@ -48,6 +48,7 @@ from pandas.core.indexes.timedeltas import TimedeltaIndex
 from pandas.core.indexing import (
     _AtIndexer,
     _iAtIndexer,
+    _IndexSliceTuple,
 )
 from pandas.core.resample import Resampler
 from pandas.core.strings import StringMethods
@@ -131,21 +132,21 @@ class _iLocIndexerSeries(_iLocIndexer, Generic[S1]):
     ) -> None: ...
 
 class _LocIndexerSeries(_LocIndexer, Generic[S1]):
+    # ignore needed because of mypy.  Overlapping, but we want to distinguish
+    # having a tuple of just scalars, versus tuples that include slices or Index
     @overload
-    def __getitem__(
+    def __getitem__(  # type: ignore[misc]
         self,
-        idx: MaskType
-        | Index
-        | Sequence[float]
-        | list[str]
-        | slice
-        | tuple[str | float | slice | Index, ...],
-    ) -> Series[S1]: ...
+        idx: Scalar | tuple[Scalar, ...],
+        # tuple case is for getting a specific element when using a MultiIndex
+    ) -> S1: ...
     @overload
     def __getitem__(
         self,
-        idx: str | float,
-    ) -> S1: ...
+        idx: MaskType | Index | Sequence[float] | list[str] | slice | _IndexSliceTuple,
+        # _IndexSliceTuple is when having a tuple that includes a slice.  Could just
+        # be s.loc[1, :], or s.loc[pd.IndexSlice[1, :]]
+    ) -> Series[S1]: ...
     @overload
     def __setitem__(
         self,

tests/test_series.py

@@ -120,9 +120,12 @@ def test_types_loc_at() -> None:
 
 
 def test_multiindex_loc() -> None:
-    s = pd.Series([1, 2, 3, 4], index=pd.MultiIndex.from_product([[1, 2], ["a", "b"]]))
-    check(assert_type(s.loc[1, :], pd.Series), pd.Series)
-    check(assert_type(s.loc[pd.Index([1]), :], pd.Series), pd.Series)
+    s = pd.Series(
+        [1, 2, 3, 4], index=pd.MultiIndex.from_product([[1, 2], ["a", "b"]]), dtype=int
+    )
+    check(assert_type(s.loc[1, :], "pd.Series[int]"), pd.Series, int)
+    check(assert_type(s.loc[pd.Index([1]), :], "pd.Series[int]"), pd.Series, int)
+    check(assert_type(s.loc[1, "a"], int), np.int_)
 
 
 def test_types_boolean_indexing() -> None: