Backport PR pandas-dev#55527: BUG fix deprecation of limit and `fil…

…l_method` in `pct_change`

doc/source/whatsnew/v2.1.2.rst

@@ -8,6 +8,14 @@ including other versions of pandas.
 
 {{ header }}
 
+.. ---------------------------------------------------------------------------
+.. _whatsnew_212.deprecations:
+
+Deprecations
+~~~~~~~~~~~~
+
+- Reverted deprecation of ``fill_method=None`` in :meth:`DataFrame.pct_change`, :meth:`Series.pct_change`, :meth:`DataFrameGroupBy.pct_change`, and :meth:`SeriesGroupBy.pct_change`; the values ``'backfill'``, ``'bfill'``, ``'pad'``, and ``'ffill'`` are still deprecated (:issue:`53491`)
+
 .. ---------------------------------------------------------------------------
 .. _whatsnew_212.regressions:
 

pandas/core/generic.py

@@ -11579,6 +11579,7 @@ def pct_change(
             How to handle NAs **before** computing percent changes.
 
             .. deprecated:: 2.1
+                All options of `fill_method` are deprecated except `fill_method=None`.
 
         limit : int, default None
             The number of consecutive NAs to fill before stopping.
@@ -11685,32 +11686,33 @@ def pct_change(
         APPL -0.252395 -0.011860   NaN
         """
         # GH#53491
-        if fill_method is not lib.no_default or limit is not lib.no_default:
+        if fill_method not in (lib.no_default, None) or limit is not lib.no_default:
             warnings.warn(
-                "The 'fill_method' and 'limit' keywords in "
-                f"{type(self).__name__}.pct_change are deprecated and will be "
-                "removed in a future version. Call "
-                f"{'bfill' if fill_method in ('backfill', 'bfill') else 'ffill'} "
-                "before calling pct_change instead.",
+                "The 'fill_method' keyword being not None and the 'limit' keyword in "
+                f"{type(self).__name__}.pct_change are deprecated and will be removed "
+                "in a future version. Either fill in any non-leading NA values prior "
+                "to calling pct_change or specify 'fill_method=None' to not fill NA "
+                "values.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
         if fill_method is lib.no_default:
-            cols = self.items() if self.ndim == 2 else [(None, self)]
-            for _, col in cols:
-                mask = col.isna().values
-                mask = mask[np.argmax(~mask) :]
-                if mask.any():
-                    warnings.warn(
-                        "The default fill_method='pad' in "
-                        f"{type(self).__name__}.pct_change is deprecated and will be "
-                        "removed in a future version. Call ffill before calling "
-                        "pct_change to retain current behavior and silence this "
-                        "warning.",
-                        FutureWarning,
-                        stacklevel=find_stack_level(),
-                    )
-                    break
+            if limit is lib.no_default:
+                cols = self.items() if self.ndim == 2 else [(None, self)]
+                for _, col in cols:
+                    mask = col.isna().values
+                    mask = mask[np.argmax(~mask) :]
+                    if mask.any():
+                        warnings.warn(
+                            "The default fill_method='pad' in "
+                            f"{type(self).__name__}.pct_change is deprecated and will "
+                            "be removed in a future version. Either fill in any "
+                            "non-leading NA values prior to calling pct_change or "
+                            "specify 'fill_method=None' to not fill NA values.",
+                            FutureWarning,
+                            stacklevel=find_stack_level(),
+                        )
+                        break
             fill_method = "pad"
         if limit is lib.no_default:
             limit = None

pandas/core/groupby/groupby.py

@@ -5217,7 +5217,7 @@ def diff(
     def pct_change(
         self,
         periods: int = 1,
-        fill_method: FillnaOptions | lib.NoDefault = lib.no_default,
+        fill_method: FillnaOptions | None | lib.NoDefault = lib.no_default,
         limit: int | None | lib.NoDefault = lib.no_default,
         freq=None,
         axis: Axis | lib.NoDefault = lib.no_default,
@@ -5269,23 +5269,26 @@ def pct_change(
         goldfish    0.2  0.125
         """
         # GH#53491
-        if fill_method is not lib.no_default or limit is not lib.no_default:
+        if fill_method not in (lib.no_default, None) or limit is not lib.no_default:
             warnings.warn(
-                "The 'fill_method' and 'limit' keywords in "
-                f"{type(self).__name__}.pct_change are deprecated and will be "
-                "removed in a future version. Call "
-                f"{'bfill' if fill_method in ('backfill', 'bfill') else 'ffill'} "
-                "before calling pct_change instead.",
+                "The 'fill_method' keyword being not None and the 'limit' keyword in "
+                f"{type(self).__name__}.pct_change are deprecated and will be removed "
+                "in a future version. Either fill in any non-leading NA values prior "
+                "to calling pct_change or specify 'fill_method=None' to not fill NA "
+                "values.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
         if fill_method is lib.no_default:
-            if any(grp.isna().values.any() for _, grp in self):
+            if limit is lib.no_default and any(
+                grp.isna().values.any() for _, grp in self
+            ):
                 warnings.warn(
                     "The default fill_method='ffill' in "
-                    f"{type(self).__name__}.pct_change is deprecated and will be "
-                    "removed in a future version. Call ffill before calling "
-                    "pct_change to retain current behavior and silence this warning.",
+                    f"{type(self).__name__}.pct_change is deprecated and will "
+                    "be removed in a future version. Either fill in any "
+                    "non-leading NA values prior to calling pct_change or "
+                    "specify 'fill_method=None' to not fill NA values.",
                     FutureWarning,
                     stacklevel=find_stack_level(),
                 )

pandas/tests/frame/methods/test_pct_change.py

@@ -29,7 +29,7 @@ def test_pct_change_with_nas(
         obj = frame_or_series(vals)
 
         msg = (
-            "The 'fill_method' and 'limit' keywords in "
+            "The 'fill_method' keyword being not None and the 'limit' keyword in "
             f"{type(obj).__name__}.pct_change are deprecated"
         )
         with tm.assert_produces_warning(FutureWarning, match=msg):
@@ -46,7 +46,7 @@ def test_pct_change_numeric(self):
         pnl.iat[2, 3] = 60
 
         msg = (
-            "The 'fill_method' and 'limit' keywords in "
+            "The 'fill_method' keyword being not None and the 'limit' keyword in "
             "DataFrame.pct_change are deprecated"
         )
 
@@ -59,12 +59,11 @@ def test_pct_change_numeric(self):
 
     def test_pct_change(self, datetime_frame):
         msg = (
-            "The 'fill_method' and 'limit' keywords in "
+            "The 'fill_method' keyword being not None and the 'limit' keyword in "
             "DataFrame.pct_change are deprecated"
         )
 
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            rs = datetime_frame.pct_change(fill_method=None)
+        rs = datetime_frame.pct_change(fill_method=None)
         tm.assert_frame_equal(rs, datetime_frame / datetime_frame.shift(1) - 1)
 
         rs = datetime_frame.pct_change(2)
@@ -110,7 +109,7 @@ def test_pct_change_periods_freq(
         self, datetime_frame, freq, periods, fill_method, limit
     ):
         msg = (
-            "The 'fill_method' and 'limit' keywords in "
+            "The 'fill_method' keyword being not None and the 'limit' keyword in "
             "DataFrame.pct_change are deprecated"
         )
 
@@ -144,11 +143,12 @@ def test_pct_change_with_duplicated_indices(fill_method):
         {0: [np.nan, 1, 2, 3, 9, 18], 1: [0, 1, np.nan, 3, 9, 18]}, index=["a", "b"] * 3
     )
 
+    warn = None if fill_method is None else FutureWarning
     msg = (
-        "The 'fill_method' and 'limit' keywords in "
+        "The 'fill_method' keyword being not None and the 'limit' keyword in "
         "DataFrame.pct_change are deprecated"
     )
-    with tm.assert_produces_warning(FutureWarning, match=msg):
+    with tm.assert_produces_warning(warn, match=msg):
         result = data.pct_change(fill_method=fill_method)
 
     if fill_method is None:

pandas/tests/groupby/transform/test_transform.py

@@ -1063,7 +1063,7 @@ def test_pct_change(frame_or_series, freq, periods, fill_method, limit):
         expected = expected.to_frame("vals")
 
     msg = (
-        "The 'fill_method' and 'limit' keywords in "
+        "The 'fill_method' keyword being not None and the 'limit' keyword in "
         f"{type(gb).__name__}.pct_change are deprecated"
     )
     with tm.assert_produces_warning(FutureWarning, match=msg):

pandas/tests/series/methods/test_pct_change.py

@@ -11,12 +11,11 @@
 class TestSeriesPctChange:
     def test_pct_change(self, datetime_series):
         msg = (
-            "The 'fill_method' and 'limit' keywords in "
+            "The 'fill_method' keyword being not None and the 'limit' keyword in "
             "Series.pct_change are deprecated"
         )
 
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            rs = datetime_series.pct_change(fill_method=None)
+        rs = datetime_series.pct_change(fill_method=None)
         tm.assert_series_equal(rs, datetime_series / datetime_series.shift(1) - 1)
 
         rs = datetime_series.pct_change(2)
@@ -69,7 +68,7 @@ def test_pct_change_periods_freq(
         self, freq, periods, fill_method, limit, datetime_series
     ):
         msg = (
-            "The 'fill_method' and 'limit' keywords in "
+            "The 'fill_method' keyword being not None and the 'limit' keyword in "
             "Series.pct_change are deprecated"
         )
 
@@ -101,8 +100,12 @@ def test_pct_change_with_duplicated_indices(fill_method):
     # GH30463
     s = Series([np.nan, 1, 2, 3, 9, 18], index=["a", "b"] * 3)
 
-    msg = "The 'fill_method' and 'limit' keywords in Series.pct_change are deprecated"
-    with tm.assert_produces_warning(FutureWarning, match=msg):
+    warn = None if fill_method is None else FutureWarning
+    msg = (
+        "The 'fill_method' keyword being not None and the 'limit' keyword in "
+        "Series.pct_change are deprecated"
+    )
+    with tm.assert_produces_warning(warn, match=msg):
         result = s.pct_change(fill_method=fill_method)
 
     expected = Series([np.nan, np.nan, 1.0, 0.5, 2.0, 1.0], index=["a", "b"] * 3)