allow apply to return an offset

Author: Dr-Irv

pandas-stubs/core/series.pyi

@@ -1030,6 +1030,14 @@ class Series(IndexOpsMixin[S1], NDFrame):
         **kwds,
     ) -> Series: ...
     @overload
+    def apply(
+        self,
+        func: Callable[..., BaseOffset],
+        convertDType: _bool = ...,
+        args: tuple = ...,
+        **kwds,
+    ) -> OffsetSeries: ...
+    @overload
     def apply(
         self,
         func: Callable[..., Series],

tests/test_series.py

@@ -3454,3 +3454,14 @@ def test_slice_timestamp() -> None:
         pd.Series,
         np.integer,
     )
+
+
+def test_apply_dateoffset() -> None:
+    # GH 454
+    months = [1, 2, 3]
+    s = pd.Series(months)
+    check(
+        assert_type(s.apply(lambda x: pd.DateOffset(months=x)), "OffsetSeries"),
+        pd.Series,
+        pd.DateOffset,
+    )