CLN: Enforce deprecation of method and limit in pct_change methods (#57742)

* CLN: Enforce deprecation of method and limit in pct_change methods

* Test fixups

* mypy fixup

Author: rhshadrach

Diff for: doc/source/whatsnew/v3.0.0.rst

@@ -228,6 +228,7 @@ Removal of prior version deprecations/changes
 - Removed ``read_gbq`` and ``DataFrame.to_gbq``. Use ``pandas_gbq.read_gbq`` and ``pandas_gbq.to_gbq`` instead https://pandas-gbq.readthedocs.io/en/latest/api.html (:issue:`55525`)
 - Removed ``use_nullable_dtypes`` from :func:`read_parquet` (:issue:`51853`)
 - Removed ``year``, ``month``, ``quarter``, ``day``, ``hour``, ``minute``, and ``second`` keywords in the :class:`PeriodIndex` constructor, use :meth:`PeriodIndex.from_fields` instead (:issue:`55960`)
+- Removed argument ``limit`` from :meth:`DataFrame.pct_change`, :meth:`Series.pct_change`, :meth:`.DataFrameGroupBy.pct_change`, and :meth:`.SeriesGroupBy.pct_change`; the argument ``method`` must be set to ``None`` and will be removed in a future version of pandas (:issue:`53520`)
 - Removed deprecated argument ``obj`` in :meth:`.DataFrameGroupBy.get_group` and :meth:`.SeriesGroupBy.get_group` (:issue:`53545`)
 - Removed deprecated behavior of :meth:`Series.agg` using :meth:`Series.apply` (:issue:`53325`)
 - Removed option ``mode.use_inf_as_na``, convert inf entries to ``NaN`` before instead (:issue:`51684`)

Diff for: pandas/core/generic.py

@@ -11122,8 +11122,7 @@ def describe(
     def pct_change(
         self,
         periods: int = 1,
-        fill_method: FillnaOptions | None | lib.NoDefault = lib.no_default,
-        limit: int | None | lib.NoDefault = lib.no_default,
+        fill_method: None = None,
         freq=None,
         **kwargs,
     ) -> Self:
@@ -11145,17 +11144,12 @@ def pct_change(
         ----------
         periods : int, default 1
             Periods to shift for forming percent change.
-        fill_method : {'backfill', 'bfill', 'pad', 'ffill', None}, default 'pad'
-            How to handle NAs **before** computing percent changes.
+        fill_method : None
+            Must be None. This argument will be removed in a future version of pandas.
 
             .. 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.
-
-            .. deprecated:: 2.1
-
         freq : DateOffset, timedelta, or str, optional
             Increment to use from time series API (e.g. 'ME' or BDay()).
         **kwargs
@@ -11262,52 +11256,18 @@ def pct_change(
         APPL -0.252395 -0.011860   NaN
         """
         # GH#53491
-        if fill_method not in (lib.no_default, None) or limit is not lib.no_default:
-            warnings.warn(
-                "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 limit is lib.no_default:
-                cols = self.items() if self.ndim == 2 else [(None, self)]
-                for _, col in cols:
-                    if len(col) > 0:
-                        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
+        if fill_method is not None:
+            raise ValueError(f"fill_method must be None; got {fill_method=}.")
 
         axis = self._get_axis_number(kwargs.pop("axis", "index"))
-        if fill_method is None:
-            data = self
-        else:
-            data = self._pad_or_backfill(fill_method, axis=axis, limit=limit)
-
-        shifted = data.shift(periods=periods, freq=freq, axis=axis, **kwargs)
+        shifted = self.shift(periods=periods, freq=freq, axis=axis, **kwargs)
         # Unsupported left operand type for / ("Self")
-        rs = data / shifted - 1  # type: ignore[operator]
+        rs = self / shifted - 1  # type: ignore[operator]
         if freq is not None:
             # Shift method is implemented differently when freq is not None
             # We want to restore the original index
             rs = rs.loc[~rs.index.duplicated()]
-            rs = rs.reindex_like(data)
+            rs = rs.reindex_like(self)
         return rs.__finalize__(self, method="pct_change")
 
     @final

Diff for: pandas/core/groupby/groupby.py

@@ -45,7 +45,6 @@ class providing the base-class of operations.
     AnyArrayLike,
     ArrayLike,
     DtypeObj,
-    FillnaOptions,
     IndexLabel,
     IntervalClosedType,
     NDFrameT,
@@ -5147,8 +5146,7 @@ def diff(
     def pct_change(
         self,
         periods: int = 1,
-        fill_method: FillnaOptions | None | lib.NoDefault = lib.no_default,
-        limit: int | None | lib.NoDefault = lib.no_default,
+        fill_method: None = None,
         freq=None,
     ):
         """
@@ -5161,19 +5159,11 @@ def pct_change(
             a period of 1 means adjacent elements are compared, whereas a period
             of 2 compares every other element.
 
-        fill_method : FillnaOptions or None, default None
-            Specifies how to handle missing values after the initial shift
-            operation necessary for percentage change calculation. Users are
-            encouraged to handle missing values manually in future versions.
-            Valid options are:
-            - A FillnaOptions value ('ffill', 'bfill') for forward or backward filling.
-            - None to avoid filling.
-            Note: Usage is discouraged due to impending deprecation.
+        fill_method : None
+            Must be None. This argument will be removed in a future version of pandas.
 
-        limit : int or None, default None
-            The maximum number of consecutive NA values to fill, based on the chosen
-            `fill_method`. Address NaN values prior to using `pct_change` as this
-            parameter is nearing deprecation.
+            .. deprecated:: 2.1
+                All options of `fill_method` are deprecated except `fill_method=None`.
 
         freq : str, pandas offset object, or None, default None
             The frequency increment for time series data (e.g., 'M' for month-end).
@@ -5227,49 +5217,24 @@ def pct_change(
         goldfish    0.2  0.125
         """
         # GH#53491
-        if fill_method not in (lib.no_default, None) or limit is not lib.no_default:
-            warnings.warn(
-                "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 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. 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(),
-                )
-            fill_method = "ffill"
-        if limit is lib.no_default:
-            limit = None
+        if fill_method is not None:
+            raise ValueError(f"fill_method must be None; got {fill_method=}.")
 
         # TODO(GH#23918): Remove this conditional for SeriesGroupBy when
         #  GH#23918 is fixed
         if freq is not None:
             f = lambda x: x.pct_change(
                 periods=periods,
-                fill_method=fill_method,
-                limit=limit,
                 freq=freq,
                 axis=0,
             )
             return self._python_apply_general(f, self._selected_obj, is_transform=True)
 
         if fill_method is None:  # GH30463
-            fill_method = "ffill"
-            limit = 0
-        filled = getattr(self, fill_method)(limit=limit)
+            op = "ffill"
+        else:
+            op = fill_method
+        filled = getattr(self, op)(limit=0)
         fill_grp = filled.groupby(self._grouper.codes, group_keys=self.group_keys)
         shifted = fill_grp.shift(periods=periods, freq=freq)
         return (filled / shifted) - 1

Diff for: pandas/tests/frame/methods/test_pct_change.py

@@ -10,30 +10,17 @@
 
 class TestDataFramePctChange:
     @pytest.mark.parametrize(
-        "periods, fill_method, limit, exp",
+        "periods, exp",
         [
-            (1, "ffill", None, [np.nan, np.nan, np.nan, 1, 1, 1.5, 0, 0]),
-            (1, "ffill", 1, [np.nan, np.nan, np.nan, 1, 1, 1.5, 0, np.nan]),
-            (1, "bfill", None, [np.nan, 0, 0, 1, 1, 1.5, np.nan, np.nan]),
-            (1, "bfill", 1, [np.nan, np.nan, 0, 1, 1, 1.5, np.nan, np.nan]),
-            (-1, "ffill", None, [np.nan, np.nan, -0.5, -0.5, -0.6, 0, 0, np.nan]),
-            (-1, "ffill", 1, [np.nan, np.nan, -0.5, -0.5, -0.6, 0, np.nan, np.nan]),
-            (-1, "bfill", None, [0, 0, -0.5, -0.5, -0.6, np.nan, np.nan, np.nan]),
-            (-1, "bfill", 1, [np.nan, 0, -0.5, -0.5, -0.6, np.nan, np.nan, np.nan]),
+            (1, [np.nan, np.nan, np.nan, 1, 1, 1.5, np.nan, np.nan]),
+            (-1, [np.nan, np.nan, -0.5, -0.5, -0.6, np.nan, np.nan, np.nan]),
         ],
     )
-    def test_pct_change_with_nas(
-        self, periods, fill_method, limit, exp, frame_or_series
-    ):
+    def test_pct_change_with_nas(self, periods, exp, frame_or_series):
         vals = [np.nan, np.nan, 1, 2, 4, 10, np.nan, np.nan]
         obj = frame_or_series(vals)
 
-        msg = (
-            "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):
-            res = obj.pct_change(periods=periods, fill_method=fill_method, limit=limit)
+        res = obj.pct_change(periods=periods)
         tm.assert_equal(res, frame_or_series(exp))
 
     def test_pct_change_numeric(self):
@@ -45,124 +32,82 @@ def test_pct_change_numeric(self):
         pnl.iat[1, 1] = np.nan
         pnl.iat[2, 3] = 60
 
-        msg = (
-            "The 'fill_method' keyword being not None and the 'limit' keyword in "
-            "DataFrame.pct_change are deprecated"
-        )
-
         for axis in range(2):
-            expected = pnl.ffill(axis=axis) / pnl.ffill(axis=axis).shift(axis=axis) - 1
-
-            with tm.assert_produces_warning(FutureWarning, match=msg):
-                result = pnl.pct_change(axis=axis, fill_method="pad")
+            expected = pnl / pnl.shift(axis=axis) - 1
+            result = pnl.pct_change(axis=axis)
             tm.assert_frame_equal(result, expected)
 
     def test_pct_change(self, datetime_frame):
-        msg = (
-            "The 'fill_method' keyword being not None and the 'limit' keyword in "
-            "DataFrame.pct_change are deprecated"
-        )
-
-        rs = datetime_frame.pct_change(fill_method=None)
+        rs = datetime_frame.pct_change()
         tm.assert_frame_equal(rs, datetime_frame / datetime_frame.shift(1) - 1)
 
         rs = datetime_frame.pct_change(2)
         filled = datetime_frame.ffill()
         tm.assert_frame_equal(rs, filled / filled.shift(2) - 1)
 
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            rs = datetime_frame.pct_change(fill_method="bfill", limit=1)
-        filled = datetime_frame.bfill(limit=1)
-        tm.assert_frame_equal(rs, filled / filled.shift(1) - 1)
+        rs = datetime_frame.pct_change()
+        tm.assert_frame_equal(rs, datetime_frame / datetime_frame.shift(1) - 1)
 
         rs = datetime_frame.pct_change(freq="5D")
-        filled = datetime_frame.ffill()
         tm.assert_frame_equal(
-            rs, (filled / filled.shift(freq="5D") - 1).reindex_like(filled)
+            rs,
+            (datetime_frame / datetime_frame.shift(freq="5D") - 1).reindex_like(
+                datetime_frame
+            ),
         )
 
     def test_pct_change_shift_over_nas(self):
         s = Series([1.0, 1.5, np.nan, 2.5, 3.0])
 
         df = DataFrame({"a": s, "b": s})
 
-        msg = "The default fill_method='pad' in DataFrame.pct_change is deprecated"
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            chg = df.pct_change()
-
-        expected = Series([np.nan, 0.5, 0.0, 2.5 / 1.5 - 1, 0.2])
+        chg = df.pct_change()
+        expected = Series([np.nan, 0.5, np.nan, np.nan, 0.2])
         edf = DataFrame({"a": expected, "b": expected})
         tm.assert_frame_equal(chg, edf)
 
     @pytest.mark.parametrize(
-        "freq, periods, fill_method, limit",
+        "freq, periods",
         [
-            ("5B", 5, None, None),
-            ("3B", 3, None, None),
-            ("3B", 3, "bfill", None),
-            ("7B", 7, "pad", 1),
-            ("7B", 7, "bfill", 3),
-            ("14B", 14, None, None),
+            ("5B", 5),
+            ("3B", 3),
+            ("14B", 14),
         ],
     )
     def test_pct_change_periods_freq(
-        self, datetime_frame, freq, periods, fill_method, limit
+        self,
+        datetime_frame,
+        freq,
+        periods,
     ):
-        msg = (
-            "The 'fill_method' keyword being not None and the 'limit' keyword in "
-            "DataFrame.pct_change are deprecated"
-        )
-
         # GH#7292
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            rs_freq = datetime_frame.pct_change(
-                freq=freq, fill_method=fill_method, limit=limit
-            )
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            rs_periods = datetime_frame.pct_change(
-                periods, fill_method=fill_method, limit=limit
-            )
+        rs_freq = datetime_frame.pct_change(freq=freq)
+        rs_periods = datetime_frame.pct_change(periods)
         tm.assert_frame_equal(rs_freq, rs_periods)
 
         empty_ts = DataFrame(index=datetime_frame.index, columns=datetime_frame.columns)
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            rs_freq = empty_ts.pct_change(
-                freq=freq, fill_method=fill_method, limit=limit
-            )
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            rs_periods = empty_ts.pct_change(
-                periods, fill_method=fill_method, limit=limit
-            )
+        rs_freq = empty_ts.pct_change(freq=freq)
+        rs_periods = empty_ts.pct_change(periods)
         tm.assert_frame_equal(rs_freq, rs_periods)
 
 
-@pytest.mark.parametrize("fill_method", ["pad", "ffill", None])
-def test_pct_change_with_duplicated_indices(fill_method):
+def test_pct_change_with_duplicated_indices():
     # GH30463
     data = DataFrame(
         {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' keyword being not None and the 'limit' keyword in "
-        "DataFrame.pct_change are deprecated"
-    )
-    with tm.assert_produces_warning(warn, match=msg):
-        result = data.pct_change(fill_method=fill_method)
+    result = data.pct_change()
 
-    if fill_method is None:
-        second_column = [np.nan, np.inf, np.nan, np.nan, 2.0, 1.0]
-    else:
-        second_column = [np.nan, np.inf, 0.0, 2.0, 2.0, 1.0]
+    second_column = [np.nan, np.inf, np.nan, np.nan, 2.0, 1.0]
     expected = DataFrame(
         {0: [np.nan, np.nan, 1.0, 0.5, 2.0, 1.0], 1: second_column},
         index=["a", "b"] * 3,
     )
     tm.assert_frame_equal(result, expected)
 
 
-def test_pct_change_none_beginning_no_warning():
+def test_pct_change_none_beginning():
     # GH#54481
     df = DataFrame(
         [