fix: constraint instead of bound to get rid of Any python/mypy#19525 (comment)

Author: cmp0xff

pandas-stubs/_typing.pyi

@@ -847,6 +847,26 @@ S1 = TypeVar("S1", bound=SeriesDType, default=Any)
 S2 = TypeVar("S2", bound=SeriesDType)
 S3 = TypeVar("S3", bound=SeriesDType)
 
+# Constraint, instead of bound
+C2 = TypeVar(
+    "C2",
+    str,
+    bytes,
+    datetime.date,
+    datetime.time,
+    bool,
+    int,
+    float,
+    complex,
+    Dtype,
+    datetime.datetime,  # includes pd.Timestamp
+    datetime.timedelta,  # includes pd.Timedelta
+    Period,
+    Interval,
+    CategoricalDtype,
+    BaseOffset,
+)
+
 IndexingInt: TypeAlias = (
     int | np.int_ | np.integer | np.unsignedinteger | np.signedinteger | np.int8
 )

pandas-stubs/core/indexes/base.pyi

@@ -42,6 +42,7 @@ from typing_extensions import (
 
 from pandas._libs.interval import _OrderableT
 from pandas._typing import (
+    C2,
     S1,
     AnyAll,
     AxesData,
@@ -402,7 +403,9 @@ class Index(IndexOpsMixin[S1]):
     @overload
     def __getitem__(self, idx: int | tuple[np_ndarray_anyint, ...]) -> S1: ...
     @overload
-    def append(self, other: Index[S1] | Sequence[Index[S1]]) -> Self: ...
+    def append(
+        self: Index[C2], other: Index[C2] | Sequence[Index[C2]]
+    ) -> Index[C2]: ...
     @overload
     def append(self, other: Index | Sequence[Index]) -> Index: ...
     def putmask(self, mask, value): ...

tests/test_indexes.py

@@ -1042,20 +1042,8 @@ def test_append_mix() -> None:
     check(assert_type(first.append([third]), pd.Index), pd.Index)
     check(assert_type(first.append([second, third]), pd.Index), pd.Index)
 
-    # mypy thinks the following two are of the type `Index[Any]`, whereas
-    # pyright recognises them as `Index[int | str]`
-    check(
-        assert_type(  # type: ignore[assert-type]
-            third.append([]), "pd.Index[int | str]"
-        ),
-        pd.Index,
-    )
-    check(
-        assert_type(  # type: ignore[assert-type]
-            third.append(cast("list[Index[Any]]", [])), "pd.Index[int | str]"
-        ),
-        pd.Index,
-    )
+    check(assert_type(third.append([]), pd.Index), pd.Index)
+    check(assert_type(third.append(cast("list[Index[Any]]", [])), pd.Index), pd.Index)
     check(assert_type(third.append([first]), pd.Index), pd.Index)
     check(assert_type(third.append([first, second]), pd.Index), pd.Index)