use typealias

Author: MarcoGorelli

pandas-stubs/_typing.pyi

@@ -576,6 +576,9 @@ S2 = TypeVar(
     | list[str],
 )
 
+UnknownSeries: TypeAlias = Series[Any]
+UnknownIndex: TypeAlias = Index[Any]
+
 IndexingInt: TypeAlias = (
     int | np.int_ | np.integer | np.unsignedinteger | np.signedinteger | np.int8
 )

pandas-stubs/core/series.pyi

@@ -2133,8 +2133,6 @@ class Series(IndexOpsMixin[S1], NDFrame):
     ) -> Self: ...
     def __bool__(self) -> NoReturn: ...
 
-class UnknownSeries(Series[Any]): ...
-
 class TimestampSeries(Series[Timestamp]):
     @property
     def dt(self) -> TimestampProperties: ...  # type: ignore[override] # pyright: ignore[reportIncompatibleMethodOverride]

pandas-stubs/core/strings.pyi

@@ -12,6 +12,7 @@ from typing import (
     overload,
 )
 
+import numpy as np
 import numpy.typing as npt
 import pandas as pd
 from pandas import (
@@ -21,8 +22,6 @@ from pandas import (
     Series,
 )
 from pandas.core.base import NoNewAttributesMixin
-from pandas.core.indexes.base import UnknownIndex
-from pandas.core.series import UnknownSeries
 
 from pandas._libs.tslibs.nattype import NaTType
 from pandas._typing import (
@@ -64,7 +63,7 @@ class StringMethods(NoNewAttributesMixin, Generic[T, _TS, _TM, _TS2]):
     def cat(
         self,
         others: (
-            UnknownSeries | UnknownIndex | pd.DataFrame | npt.NDArray[Any] | list[Any]
+            Series[str] | Index[str] | pd.DataFrame | npt.NDArray[np.str_] | list[str]
         ),
         sep: str = ...,
         na_rep: str | None = ...,
@@ -167,7 +166,7 @@ class StringMethods(NoNewAttributesMixin, Generic[T, _TS, _TM, _TS2]):
     def count(self, pat: str, flags: int = ...) -> Series[int]: ...
     def startswith(self, pat: str | tuple[str, ...], na: Any = ...) -> Series[bool]: ...
     def endswith(self, pat: str | tuple[str, ...], na: Any = ...) -> Series[bool]: ...
-    def findall(self, pat: str, flags: int = ...) -> UnknownSeries: ...
+    def findall(self, pat: str, flags: int = ...) -> Series[list[str]]: ...
     @overload
     def extract(
         self, pat: str, flags: int = ..., *, expand: Literal[True] = ...

tests/test_series.py

@@ -67,14 +67,15 @@
         TimestampSeries,
     )
 
+    from pandas._typing import UnknownSeries
+
 else:
     TimedeltaSeries: TypeAlias = pd.Series
     TimestampSeries: TypeAlias = pd.Series
     OffsetSeries: TypeAlias = pd.Series
+    UnknownSeries: TypeAlias = pd.Series
 
 if TYPE_CHECKING:
-    from pandas.core.series import UnknownSeries  # noqa: F401
-
     from pandas._typing import (
         BooleanDtypeArg,
         BytesDtypeArg,
@@ -91,6 +92,7 @@
     )
     from pandas._typing import np_ndarray_int  # noqa: F401
 
+
 # Tests will use numpy 2.1 in python 3.10 or later
 # From Numpy 2.1 __init__.pyi
 _DTypeKind: TypeAlias = Literal[
@@ -1597,7 +1599,7 @@ def test_string_accessors():
     check(assert_type(s3.str.extract(r"([ab])?(\d)"), pd.DataFrame), pd.DataFrame)
     check(assert_type(s3.str.extractall(r"([ab])?(\d)"), pd.DataFrame), pd.DataFrame)
     check(assert_type(s.str.find("p"), pd.Series), pd.Series)
-    check(assert_type(s.str.findall("pp"), "UnknownSeries"), pd.Series)
+    check(assert_type(s.str.findall("pp"), "pd.Series[list[str]]"), pd.Series, list)
     check(assert_type(s.str.fullmatch("apple"), "pd.Series[bool]"), pd.Series, np.bool_)
     check(assert_type(s.str.get(2), pd.Series), pd.Series)
     check(assert_type(s.str.get_dummies(), pd.DataFrame), pd.DataFrame)
@@ -1668,8 +1670,17 @@ def test_series_overloads_cat():
     check(assert_type(s.str.cat(sep=";"), str), str)
     check(assert_type(s.str.cat(None, sep=";"), str), str)
     check(
-        assert_type(s.str.cat(["A", "B", "C", "D", "E", "F", "G"], sep=";"), pd.Series),
-        pd.Series,
+        assert_type(
+            s.str.cat(["A", "B", "C", "D", "E", "F", "G"], sep=";"), UnknownSeries
+        ),
+        UnknownSeries,
+    )
+    check(
+        assert_type(
+            s.str.cat(pd.Series(["A", "B", "C", "D", "E", "F", "G"]), sep=";"),
+            UnknownSeries,
+        ),
+        UnknownSeries,
     )