GH456 PR Feedback

Author: loicdiridollou

pandas-stubs/core/groupby/generic.pyi

@@ -71,6 +71,15 @@ class SeriesGroupBy(GroupBy[Series[S1]], Generic[S1, ByT]):
         **kwargs,
     ) -> Series[S2]: ...
     @overload
+    def aggregate(
+        self,
+        func: Callable[[Series], S2],
+        *args,
+        engine: WindowingEngine = ...,
+        engine_kwargs: WindowingEngineKwargs = ...,
+        **kwargs,
+    ) -> Series[S2]: ...
+    @overload
     def aggregate(
         self,
         func: list[AggFuncTypeBase],

tests/test_series.py

@@ -1119,6 +1119,20 @@ def transform_func(
         pd.Series,
         float,
     )
+    check(
+        assert_type(
+            s.groupby(lambda x: x).transform("mean"),
+            "pd.Series",
+        ),
+        pd.Series,
+    )
+    check(
+        assert_type(
+            s.groupby(lambda x: x).transform("first"),
+            "pd.Series",
+        ),
+        pd.Series,
+    )
 
 
 def test_types_groupby_aggregate() -> None: