From 8794b35d5eb8a7fd7d813fdcc073eed995284a9d Mon Sep 17 00:00:00 2001
From: Stephen Randall <stephen.randall@jhuapl.edu>
Date: Fri, 20 Jun 2025 00:27:09 -0400
Subject: [PATCH 1/3] update types, add tests

---
 pandas-stubs/core/frame.pyi  |  6 +++---
 pandas-stubs/core/series.pyi |  2 +-
 tests/test_frame.py          |  7 +++++++
 tests/test_series.py         | 13 ++++++++++++-
 4 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/pandas-stubs/core/frame.pyi b/pandas-stubs/core/frame.pyi
index 2a9875d8..90560dc2 100644
--- a/pandas-stubs/core/frame.pyi
+++ b/pandas-stubs/core/frame.pyi
@@ -1317,18 +1317,18 @@ class DataFrame(NDFrame, OpsMixin, _GetItemHack):
     ) -> Self: ...
     @overload
     def stack(
-        self, level: Level | list[Level] = ..., dropna: _bool = ..., sort: _bool = ...
+        self, level: IndexLabel = ..., dropna: _bool = ..., sort: _bool = ...
     ) -> Self | Series: ...
     @overload
     def stack(
-        self, level: Level | list[Level] = ..., future_stack: _bool = ...
+        self, level: IndexLabel = ..., future_stack: _bool = ...
     ) -> Self | Series: ...
     def explode(
         self, column: Sequence[Hashable], ignore_index: _bool = ...
     ) -> Self: ...
     def unstack(
         self,
-        level: Level = ...,
+        level: IndexLabel = ...,
         fill_value: Scalar | None = ...,
         sort: _bool = ...,
     ) -> Self | Series: ...
diff --git a/pandas-stubs/core/series.pyi b/pandas-stubs/core/series.pyi
index 22ef5c76..1982d54b 100644
--- a/pandas-stubs/core/series.pyi
+++ b/pandas-stubs/core/series.pyi
@@ -934,7 +934,7 @@ class Series(IndexOpsMixin[S1], NDFrame):
     def explode(self) -> Series[S1]: ...
     def unstack(
         self,
-        level: Level = ...,
+        level: IndexLabel = ...,
         fill_value: int | _str | dict | None = ...,
     ) -> DataFrame: ...
     @overload
diff --git a/tests/test_frame.py b/tests/test_frame.py
index a951c8aa..f11ba634 100644
--- a/tests/test_frame.py
+++ b/tests/test_frame.py
@@ -3124,6 +3124,12 @@ def test_frame_stack() -> None:
             assert_type(df_multi_level_cols2.stack(0), Union[pd.DataFrame, pd.Series]),
             pd.DataFrame,
         )
+        check(
+            assert_type(
+                df_multi_level_cols2.stack([0]), Union[pd.DataFrame, pd.Series]
+            ),
+            pd.DataFrame,
+        )
         check(
             assert_type(
                 df_multi_level_cols2.stack([0, 1]),
@@ -4461,6 +4467,7 @@ def test_unstack() -> None:
     ).set_index([0, 1])
 
     check(assert_type(df.unstack(0), pd.DataFrame | pd.Series), pd.DataFrame)
+    check(assert_type(df.unstack([0]), pd.DataFrame | pd.Series), pd.DataFrame)
     check(
         assert_type(
             df.unstack(1, fill_value=pd.Timestamp(2023, 4, 5)), pd.DataFrame | pd.Series
diff --git a/tests/test_series.py b/tests/test_series.py
index a2ace21e..8b981070 100644
--- a/tests/test_series.py
+++ b/tests/test_series.py
@@ -3902,7 +3902,6 @@ def test_series_items() -> None:
 
 
 def test_cumsum_timedelta() -> None:
-
     s = pd.Series(pd.to_timedelta([1, 2, 3], "h"))
     check(assert_type(s.cumsum(), "TimedeltaSeries"), pd.Series, pd.Timedelta)
     check(
@@ -3910,3 +3909,15 @@ def test_cumsum_timedelta() -> None:
         pd.Series,
         pd.Timestamp,
     )
+
+
+def test_series_unstack() -> None:
+    df = pd.DataFrame([[1, 3, 5], [2, 4, 6]])
+    s = df.transpose().stack([*range(df.index.nlevels)])
+    check(
+        assert_type(
+            s.unstack([*range(s.index.nlevels // 2)]),
+            Union[pd.Series, pd.DataFrame],
+        ),
+        pd.DataFrame,
+    )

From be32ee12d99485329340a03a2a61694f1b419040 Mon Sep 17 00:00:00 2001
From: Stephen Randall <stephen.randall@jhuapl.edu>
Date: Fri, 20 Jun 2025 00:31:10 -0400
Subject: [PATCH 2/3] remove unnecessary test

---
 tests/test_frame.py | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/tests/test_frame.py b/tests/test_frame.py
index f11ba634..d58bd7f8 100644
--- a/tests/test_frame.py
+++ b/tests/test_frame.py
@@ -3124,12 +3124,6 @@ def test_frame_stack() -> None:
             assert_type(df_multi_level_cols2.stack(0), Union[pd.DataFrame, pd.Series]),
             pd.DataFrame,
         )
-        check(
-            assert_type(
-                df_multi_level_cols2.stack([0]), Union[pd.DataFrame, pd.Series]
-            ),
-            pd.DataFrame,
-        )
         check(
             assert_type(
                 df_multi_level_cols2.stack([0, 1]),

From 486f88875baf1c4ac14d5993f79392b6d382dca9 Mon Sep 17 00:00:00 2001
From: Stephen Randall <stephen.randall@jhuapl.edu>
Date: Fri, 20 Jun 2025 16:38:22 -0400
Subject: [PATCH 3/3] added check

---
 tests/test_series.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tests/test_series.py b/tests/test_series.py
index 8b981070..3f25d981 100644
--- a/tests/test_series.py
+++ b/tests/test_series.py
@@ -3914,6 +3914,7 @@ def test_cumsum_timedelta() -> None:
 def test_series_unstack() -> None:
     df = pd.DataFrame([[1, 3, 5], [2, 4, 6]])
     s = df.transpose().stack([*range(df.index.nlevels)])
+    check(assert_type(s, Union[pd.Series, pd.DataFrame]), pd.Series)
     check(
         assert_type(
             s.unstack([*range(s.index.nlevels // 2)]),