fix return type of series pct_change, add test for series.pct_change

Author: yangdanny97

pandas-stubs/core/series.pyi

@@ -1553,7 +1553,7 @@ class Series(IndexOpsMixin[S1], NDFrame):
         freq: DateOffset | timedelta | _str | None = ...,
         *,
         fill_value: Scalar | NAType | None = ...,
-    ) -> Series[S1]: ...
+    ) -> Series[float]: ...
     def first_valid_index(self) -> Scalar: ...
     def last_valid_index(self) -> Scalar: ...
     @overload

tests/test_frame.py

@@ -2428,10 +2428,13 @@ def test_groupby_series_methods() -> None:
 
 def test_dataframe_pct_change() -> None:
     df = pd.DataFrame({"x": [1, 2, 2, 3, 3], "y": [10, 20, 30, 40, 50]})
-    df.pct_change()
-    df.pct_change(fill_method=None)
-    df.pct_change(axis="columns", periods=-1)
-    df.pct_change(fill_value=0)
+    check(assert_type(df.pct_change(), pd.DataFrame), pd.DataFrame)
+    check(assert_type(df.pct_change(fill_method=None), pd.DataFrame), pd.DataFrame)
+    check(
+        assert_type(df.pct_change(axis="columns", periods=-1), pd.DataFrame),
+        pd.DataFrame,
+    )
+    check(assert_type(df.pct_change(fill_value=0), pd.DataFrame), pd.DataFrame)
 
 
 def test_indexslice_setitem():

tests/test_series.py

@@ -441,6 +441,26 @@ def test_types_shift() -> None:
     check(assert_type(s.shift(freq="1D"), pd.Series), pd.Series, np.integer)
 
 
+def test_series_pct_change() -> None:
+    s = pd.Series([1, 2, 3], index=pd.date_range("2020", periods=3))
+    check(assert_type(s.pct_change(), "pd.Series[float]"), pd.Series, np.floating)
+    check(
+        assert_type(s.pct_change(fill_method=None), "pd.Series[float]"),
+        pd.Series,
+        np.floating,
+    )
+    check(
+        assert_type(s.pct_change(periods=-1), "pd.Series[float]"),
+        pd.Series,
+        np.floating,
+    )
+    check(
+        assert_type(s.pct_change(fill_value=0), "pd.Series[float]"),
+        pd.Series,
+        np.floating,
+    )
+
+
 def test_types_rank() -> None:
     s = pd.Series([1, 1, 2, 5, 6, np.nan])
     s.rank()