type datetimeindex max/min reductions (#1134)

Author: MarcoGorelli

pandas-stubs/core/indexes/datetimelike.pyi

@@ -1,10 +1,12 @@
+import numpy as np
 from pandas.core.indexes.extension import ExtensionIndex
 from pandas.core.indexes.timedeltas import TimedeltaIndex
 from typing_extensions import Self
 
 from pandas._libs.tslibs import BaseOffset
 from pandas._typing import (
     S1,
+    AxisIndex,
     TimeUnit,
 )
 
@@ -15,10 +17,18 @@ class DatetimeIndexOpsMixin(ExtensionIndex[S1]):
     def freqstr(self) -> str | None: ...
     @property
     def is_all_dates(self) -> bool: ...
-    def min(self, axis=..., skipna: bool = ..., *args, **kwargs): ...
-    def argmin(self, axis=..., skipna: bool = ..., *args, **kwargs): ...
-    def max(self, axis=..., skipna: bool = ..., *args, **kwargs): ...
-    def argmax(self, axis=..., skipna: bool = ..., *args, **kwargs): ...
+    def min(
+        self, axis: AxisIndex | None = ..., skipna: bool = ..., *args, **kwargs
+    ) -> S1: ...
+    def argmin(
+        self, axis: AxisIndex | None = ..., skipna: bool = ..., *args, **kwargs
+    ) -> np.int64: ...
+    def max(
+        self, axis: AxisIndex | None = ..., skipna: bool = ..., *args, **kwargs
+    ) -> S1: ...
+    def argmax(
+        self, axis: AxisIndex | None = ..., skipna: bool = ..., *args, **kwargs
+    ) -> np.int64: ...
     def __rsub__(  # type: ignore[override] # pyright: ignore[reportIncompatibleMethodOverride]
         self, other: DatetimeIndexOpsMixin
     ) -> TimedeltaIndex: ...

tests/test_indexes.py

@@ -1264,3 +1264,11 @@ def test_disallow_empty_index() -> None:
     # From GH 826
     if TYPE_CHECKING_INVALID_USAGE:
         i0 = pd.Index()  # type: ignore[call-overload] # pyright: ignore[reportCallIssue]
+
+
+def test_datetime_index_max_min_reductions() -> None:
+    dtidx = pd.DatetimeIndex(["2020-01-01", "2020-01-02"])
+    check(assert_type(dtidx.argmax(), np.int64), np.int64)
+    check(assert_type(dtidx.argmin(), np.int64), np.int64)
+    check(assert_type(dtidx.max(), pd.Timestamp), pd.Timestamp)
+    check(assert_type(dtidx.min(), pd.Timestamp), pd.Timestamp)