BUG: Fix MultiIndex.dtypes (#597) (#603)

* Fix MultiIndex.dtypes (#597)

* Tighten the MultiIndex.dtypes return value to Dtype

Author: johannes-mueller

pandas-stubs/_typing.pyi

@@ -306,6 +306,7 @@ S1 = TypeVar(
     int,
     float,
     complex,
+    Dtype,
     Timestamp,
     Timedelta,
     Period,

pandas-stubs/core/indexes/multi.pyi

@@ -15,6 +15,7 @@ from typing_extensions import Self
 
 from pandas._typing import (
     T1,
+    Dtype,
     DtypeArg,
     HashableT,
     np_ndarray_anyint,
@@ -68,6 +69,8 @@ class MultiIndex(Index):
     def __contains__(self, key) -> bool: ...
     @property
     def dtype(self) -> np.dtype: ...
+    @property
+    def dtypes(self) -> pd.Series[Dtype]: ...
     def memory_usage(self, deep: bool = ...) -> int: ...
     @property
     def nbytes(self) -> int: ...

tests/test_indexes.py

@@ -15,6 +15,7 @@
     assert_type,
 )
 
+from pandas._typing import Dtype  # noqa: F401
 from pandas._typing import Scalar
 
 from tests import (
@@ -854,3 +855,9 @@ def test_getitem() -> None:
     check(assert_type(i0, pd.Index), pd.Index)
     check(assert_type(i0[0], Scalar), str)
     check(assert_type(i0[[0, 2]], pd.Index), pd.Index, str)
+
+
+def test_multiindex_dtypes():
+    # GH-597
+    mi = pd.MultiIndex.from_tuples([(1, 2.0), (2, 3.0)], names=["foo", "bar"])
+    check(assert_type(mi.dtypes, "pd.Series[Dtype]"), pd.Series)