GH1241 Add cumsum method on TimedeltaSeries (#1243)

Author: loicdiridollou

pandas-stubs/core/series.pyi

@@ -2334,6 +2334,13 @@ class TimedeltaSeries(Series[Timedelta]):
         **kwargs: Any,
     ) -> Timedelta: ...
     def diff(self, periods: int = ...) -> TimedeltaSeries: ...  # type: ignore[override] # pyright: ignore[reportIncompatibleMethodOverride]
+    def cumsum(
+        self,
+        axis: AxisIndex | None = ...,
+        skipna: _bool = ...,
+        *args: Any,
+        **kwargs: Any,
+    ) -> TimedeltaSeries: ...
 
 class PeriodSeries(Series[Period]):
     @property

tests/test_series.py

@@ -3813,3 +3813,14 @@ def test_series_items() -> None:
     s = pd.Series(data=[1, 2, 3, 4], index=["cow", "coal", "coalesce", ""])
     check(assert_type(next(s.items()), tuple[Hashable, int]), tuple)
     check(assert_type(s.items(), Iterator[tuple[Hashable, int]]), Iterator)
+
+
+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(
+        assert_type(pd.Timestamp(0) + s.cumsum(), "TimestampSeries"),
+        pd.Series,
+        pd.Timestamp,
+    )