From dea36ba5115ebea1a9c0843626fbc0a31f50183d Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Sun, 4 Jun 2023 23:45:40 +0800
Subject: [PATCH 01/13] DEPR fill_method and limit keywords in DataFrame/Series
 pct_change

---
 pandas/core/generic.py                        | 27 +++++++-
 pandas/tests/frame/methods/test_pct_change.py | 66 +++++++++++++++----
 .../tests/series/methods/test_pct_change.py   | 46 +++++++++----
 3 files changed, 111 insertions(+), 28 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 90a0444872ec7..0704cf3d1dae1 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -11143,8 +11143,8 @@ def describe(
     def pct_change(
         self,
         periods: int = 1,
-        fill_method: Literal["backfill", "bfill", "pad", "ffill"] | None = "pad",
-        limit: int | None = None,
+        fill_method: FillnaOptions | None | lib.NoDefault = lib.no_default,
+        limit: int | None | lib.NoDefault = lib.no_default,
         freq=None,
         **kwargs,
     ) -> Self:
@@ -11168,8 +11168,14 @@ def pct_change(
             Periods to shift for forming percent change.
         fill_method : {'backfill', 'bfill', 'pad', 'ffill', None}, default 'pad'
             How to handle NAs **before** computing percent changes.
+
+            .. deprecated:: 2.1
+
         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. 'M' or BDay()).
         **kwargs
@@ -11222,7 +11228,7 @@ def pct_change(
         3    85.0
         dtype: float64
 
-        >>> s.pct_change(fill_method='ffill')
+        >>> s.fillna(method='ffill').pct_change()
         0         NaN
         1    0.011111
         2    0.000000
@@ -11269,6 +11275,21 @@ def pct_change(
         GOOG  0.179241  0.094112   NaN
         APPL -0.252395 -0.011860   NaN
         """
+        if fill_method is not lib.no_default or limit is not lib.no_default:
+            # GH#53491
+            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 fillna directly before "
+                "calling pct_change instead.",
+                FutureWarning,
+                stacklevel=find_stack_level(),
+            )
+        if fill_method is lib.no_default:
+            fill_method = "pad"
+        if limit is lib.no_default:
+            limit = None
+
         axis = self._get_axis_number(kwargs.pop("axis", "index"))
         if fill_method is None:
             data = self
diff --git a/pandas/tests/frame/methods/test_pct_change.py b/pandas/tests/frame/methods/test_pct_change.py
index a9699f8d15146..d53631e75587d 100644
--- a/pandas/tests/frame/methods/test_pct_change.py
+++ b/pandas/tests/frame/methods/test_pct_change.py
@@ -10,7 +10,7 @@
 
 class TestDataFramePctChange:
     @pytest.mark.parametrize(
-        "periods,fill_method,limit,exp",
+        "periods, fill_method, limit, 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]),
@@ -28,7 +28,12 @@ def test_pct_change_with_nas(
         vals = [np.nan, np.nan, 1, 2, 4, 10, np.nan, np.nan]
         obj = frame_or_series(vals)
 
-        res = obj.pct_change(periods=periods, fill_method=fill_method, limit=limit)
+        msg = (
+            "The 'fill_method' and 'limit' keywords 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)
         tm.assert_equal(res, frame_or_series(exp))
 
     def test_pct_change_numeric(self):
@@ -40,21 +45,34 @@ def test_pct_change_numeric(self):
         pnl.iat[1, 1] = np.nan
         pnl.iat[2, 3] = 60
 
+        msg = (
+            "The 'fill_method' and 'limit' keywords in "
+            "DataFrame.pct_change are deprecated"
+        )
+
         for axis in range(2):
             expected = pnl.ffill(axis=axis) / pnl.ffill(axis=axis).shift(axis=axis) - 1
-            result = pnl.pct_change(axis=axis, fill_method="pad")
 
+            with tm.assert_produces_warning(FutureWarning, match=msg):
+                result = pnl.pct_change(axis=axis, fill_method="pad")
             tm.assert_frame_equal(result, expected)
 
     def test_pct_change(self, datetime_frame):
-        rs = datetime_frame.pct_change(fill_method=None)
+        msg = (
+            "The 'fill_method' and 'limit' keywords in "
+            "DataFrame.pct_change are deprecated"
+        )
+
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            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)
         filled = datetime_frame.fillna(method="pad")
         tm.assert_frame_equal(rs, filled / filled.shift(2) - 1)
 
-        rs = datetime_frame.pct_change(fill_method="bfill", limit=1)
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rs = datetime_frame.pct_change(fill_method="bfill", limit=1)
         filled = datetime_frame.fillna(method="bfill", limit=1)
         tm.assert_frame_equal(rs, filled / filled.shift(1) - 1)
 
@@ -88,18 +106,31 @@ def test_pct_change_shift_over_nas(self):
     def test_pct_change_periods_freq(
         self, datetime_frame, freq, periods, fill_method, limit
     ):
-        # GH#7292
-        rs_freq = datetime_frame.pct_change(
-            freq=freq, fill_method=fill_method, limit=limit
-        )
-        rs_periods = datetime_frame.pct_change(
-            periods, fill_method=fill_method, limit=limit
+        msg = (
+            "The 'fill_method' and 'limit' keywords 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
+            )
         tm.assert_frame_equal(rs_freq, rs_periods)
 
         empty_ts = DataFrame(index=datetime_frame.index, columns=datetime_frame.columns)
-        rs_freq = empty_ts.pct_change(freq=freq, fill_method=fill_method, limit=limit)
-        rs_periods = empty_ts.pct_change(periods, fill_method=fill_method, limit=limit)
+        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
+            )
         tm.assert_frame_equal(rs_freq, rs_periods)
 
 
@@ -109,7 +140,14 @@ def test_pct_change_with_duplicated_indices(fill_method):
     data = DataFrame(
         {0: [np.nan, 1, 2, 3, 9, 18], 1: [0, 1, np.nan, 3, 9, 18]}, index=["a", "b"] * 3
     )
-    result = data.pct_change(fill_method=fill_method)
+
+    msg = (
+        "The 'fill_method' and 'limit' keywords in "
+        "DataFrame.pct_change are deprecated"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = data.pct_change(fill_method=fill_method)
+
     if fill_method is None:
         second_column = [np.nan, np.inf, np.nan, np.nan, 2.0, 1.0]
     else:
diff --git a/pandas/tests/series/methods/test_pct_change.py b/pandas/tests/series/methods/test_pct_change.py
index 017fef5fdb31f..51447fc0283aa 100644
--- a/pandas/tests/series/methods/test_pct_change.py
+++ b/pandas/tests/series/methods/test_pct_change.py
@@ -10,14 +10,21 @@
 
 class TestSeriesPctChange:
     def test_pct_change(self, datetime_series):
-        rs = datetime_series.pct_change(fill_method=None)
+        msg = (
+            "The 'fill_method' and 'limit' keywords in "
+            "Series.pct_change are deprecated"
+        )
+
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            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)
         filled = datetime_series.fillna(method="pad")
         tm.assert_series_equal(rs, filled / filled.shift(2) - 1)
 
-        rs = datetime_series.pct_change(fill_method="bfill", limit=1)
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rs = datetime_series.pct_change(fill_method="bfill", limit=1)
         filled = datetime_series.fillna(method="bfill", limit=1)
         tm.assert_series_equal(rs, filled / filled.shift(1) - 1)
 
@@ -58,18 +65,31 @@ def test_pct_change_shift_over_nas(self):
     def test_pct_change_periods_freq(
         self, freq, periods, fill_method, limit, datetime_series
     ):
-        # GH#7292
-        rs_freq = datetime_series.pct_change(
-            freq=freq, fill_method=fill_method, limit=limit
-        )
-        rs_periods = datetime_series.pct_change(
-            periods, fill_method=fill_method, limit=limit
+        msg = (
+            "The 'fill_method' and 'limit' keywords in "
+            "Series.pct_change are deprecated"
         )
+
+        # GH#7292
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rs_freq = datetime_series.pct_change(
+                freq=freq, fill_method=fill_method, limit=limit
+            )
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rs_periods = datetime_series.pct_change(
+                periods, fill_method=fill_method, limit=limit
+            )
         tm.assert_series_equal(rs_freq, rs_periods)
 
         empty_ts = Series(index=datetime_series.index, dtype=object)
-        rs_freq = empty_ts.pct_change(freq=freq, fill_method=fill_method, limit=limit)
-        rs_periods = empty_ts.pct_change(periods, fill_method=fill_method, limit=limit)
+        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
+            )
         tm.assert_series_equal(rs_freq, rs_periods)
 
 
@@ -77,6 +97,10 @@ def test_pct_change_periods_freq(
 def test_pct_change_with_duplicated_indices(fill_method):
     # GH30463
     s = Series([np.nan, 1, 2, 3, 9, 18], index=["a", "b"] * 3)
-    result = s.pct_change(fill_method=fill_method)
+
+    msg = "The 'fill_method' and 'limit' keywords in Series.pct_change are deprecated"
+    with tm.assert_produces_warning(FutureWarning, 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)
     tm.assert_series_equal(result, expected)

From b9620252a2c923a7cdf3e4d038740930eb76b3ca Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Mon, 5 Jun 2023 00:05:30 +0800
Subject: [PATCH 02/13] DEPR fill_method and limit keywords in GroupBy
 pct_change

---
 pandas/core/groupby/groupby.py                | 19 +++++++++++++++++--
 .../tests/groupby/transform/test_transform.py |  9 +++++++--
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index caed6c9747d3b..d7d24940a0885 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -3945,8 +3945,8 @@ def diff(
     def pct_change(
         self,
         periods: int = 1,
-        fill_method: FillnaOptions = "ffill",
-        limit: int | None = None,
+        fill_method: FillnaOptions | lib.NoDefault = lib.no_default,
+        limit: int | None | lib.NoDefault = lib.no_default,
         freq=None,
         axis: Axis | lib.NoDefault = lib.no_default,
     ):
@@ -3958,6 +3958,21 @@ def pct_change(
         Series or DataFrame
             Percentage changes within each group.
         """
+        if fill_method is not lib.no_default or limit is not lib.no_default:
+            # GH#53491
+            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 fillna directly before "
+                "calling pct_change instead.",
+                FutureWarning,
+                stacklevel=find_stack_level(),
+            )
+        if fill_method is lib.no_default:
+            fill_method = "ffill"
+        if limit is lib.no_default:
+            limit = None
+
         if axis is not lib.no_default:
             axis = self.obj._get_axis_number(axis)
             self._deprecate_axis(axis, "pct_change")
diff --git a/pandas/tests/groupby/transform/test_transform.py b/pandas/tests/groupby/transform/test_transform.py
index 09b24284d3b37..6f67a5aae03ba 100644
--- a/pandas/tests/groupby/transform/test_transform.py
+++ b/pandas/tests/groupby/transform/test_transform.py
@@ -969,9 +969,14 @@ def test_pct_change(frame_or_series, freq, periods, fill_method, limit):
     else:
         expected = expected.to_frame("vals")
 
-    result = gb.pct_change(
-        periods=periods, fill_method=fill_method, limit=limit, freq=freq
+    msg = (
+        "The 'fill_method' and 'limit' keywords in "
+        f"{type(gb).__name__}.pct_change are deprecated"
     )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = gb.pct_change(
+            periods=periods, fill_method=fill_method, limit=limit, freq=freq
+        )
     tm.assert_equal(result, expected)
 
 

From 59ddbc6236aa0ab0072972d6d4ca16254f9dba1e Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Mon, 5 Jun 2023 00:09:09 +0800
Subject: [PATCH 03/13] changelog added

---
 doc/source/whatsnew/v2.1.0.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/source/whatsnew/v2.1.0.rst b/doc/source/whatsnew/v2.1.0.rst
index 92124a536fe26..b97d5ea7ce1f4 100644
--- a/doc/source/whatsnew/v2.1.0.rst
+++ b/doc/source/whatsnew/v2.1.0.rst
@@ -223,6 +223,7 @@ Other API changes
 Deprecations
 ~~~~~~~~~~~~
 - Deprecated 'broadcast_axis' keyword in :meth:`Series.align` and :meth:`DataFrame.align`, upcast before calling ``align`` with ``left = DataFrame({col: left for col in right.columns}, index=right.index)`` (:issue:`51856`)
+- Deprecated 'fill_method' and 'limit' keywords in :meth:`DataFrame.pct_change`, :meth:`Series.pct_change`, :meth:`DataFrameGroupBy.pct_change`, and :meth:`SeriesGroupBy.pct_change`, explicitly call ``fillna`` before calling ``pct_change`` instead (:issue:`53491`)
 - Deprecated 'method', 'limit', and 'fill_axis' keywords in :meth:`DataFrame.align` and :meth:`Series.align`, explicitly call ``fillna`` on the alignment results instead (:issue:`51856`)
 - Deprecated 'quantile' keyword in :meth:`Rolling.quantile` and :meth:`Expanding.quantile`, renamed as 'q' instead (:issue:`52550`)
 - Deprecated :meth:`.DataFrameGroupBy.apply` and methods on the objects returned by :meth:`.DataFrameGroupBy.resample` operating on the grouping column(s); select the columns to operate on after groupby to either explicitly include or exclude the groupings and avoid the ``FutureWarning`` (:issue:`7155`)

From fda3770f2aae8a45c4b4269a769a4f4b1b9f23dc Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Mon, 5 Jun 2023 17:07:34 +0800
Subject: [PATCH 04/13] DataFrame/Series pct_change only deprecate default

---
 pandas/core/generic.py                        | 21 ++---
 pandas/tests/frame/methods/test_pct_change.py | 78 ++++++-------------
 2 files changed, 34 insertions(+), 65 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 0704cf3d1dae1..1f5ba8fe0a890 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -11144,7 +11144,7 @@ def pct_change(
         self,
         periods: int = 1,
         fill_method: FillnaOptions | None | lib.NoDefault = lib.no_default,
-        limit: int | None | lib.NoDefault = lib.no_default,
+        limit: int | None = None,
         freq=None,
         **kwargs,
     ) -> Self:
@@ -11275,20 +11275,21 @@ def pct_change(
         GOOG  0.179241  0.094112   NaN
         APPL -0.252395 -0.011860   NaN
         """
-        if fill_method is not lib.no_default or limit is not lib.no_default:
-            # GH#53491
+        # GH#53491: deprecate default fill_method=False
+        # TODO: In 3.x, change default fill_method=None, then also in 3.x
+        # deprecate the fill_method and limit keywords, and finally remove
+        # them in 4.x
+        if fill_method is 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 fillna directly before "
-                "calling pct_change instead.",
+                f"The default fill_method='pad' in {type(self).__name__}.pct_change "
+                "is deprecated and will be changed to None in a future version of "
+                "pandas. Pass fill_method='pad' to retain current behavior or "
+                "fill_method=None to adopt the future default and silence this "
+                "warning.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
-        if fill_method is lib.no_default:
             fill_method = "pad"
-        if limit is lib.no_default:
-            limit = None
 
         axis = self._get_axis_number(kwargs.pop("axis", "index"))
         if fill_method is None:
diff --git a/pandas/tests/frame/methods/test_pct_change.py b/pandas/tests/frame/methods/test_pct_change.py
index d53631e75587d..9ad61693ee608 100644
--- a/pandas/tests/frame/methods/test_pct_change.py
+++ b/pandas/tests/frame/methods/test_pct_change.py
@@ -10,7 +10,7 @@
 
 class TestDataFramePctChange:
     @pytest.mark.parametrize(
-        "periods, fill_method, limit, exp",
+        "periods,fill_method,limit,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]),
@@ -28,12 +28,7 @@ def test_pct_change_with_nas(
         vals = [np.nan, np.nan, 1, 2, 4, 10, np.nan, np.nan]
         obj = frame_or_series(vals)
 
-        msg = (
-            "The 'fill_method' and 'limit' keywords 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, fill_method=fill_method, limit=limit)
         tm.assert_equal(res, frame_or_series(exp))
 
     def test_pct_change_numeric(self):
@@ -45,38 +40,28 @@ def test_pct_change_numeric(self):
         pnl.iat[1, 1] = np.nan
         pnl.iat[2, 3] = 60
 
-        msg = (
-            "The 'fill_method' and 'limit' keywords 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")
+            result = pnl.pct_change(axis=axis, fill_method="pad")
             tm.assert_frame_equal(result, expected)
 
     def test_pct_change(self, datetime_frame):
-        msg = (
-            "The 'fill_method' and 'limit' keywords in "
-            "DataFrame.pct_change are deprecated"
-        )
+        msg = "The default fill_method='pad' in DataFrame.pct_change is 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)
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rs = datetime_frame.pct_change(2)
         filled = datetime_frame.fillna(method="pad")
         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)
+        rs = datetime_frame.pct_change(fill_method="bfill", limit=1)
         filled = datetime_frame.fillna(method="bfill", limit=1)
         tm.assert_frame_equal(rs, filled / filled.shift(1) - 1)
 
-        rs = datetime_frame.pct_change(freq="5D")
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rs = datetime_frame.pct_change(freq="5D")
         filled = datetime_frame.fillna(method="pad")
         tm.assert_frame_equal(
             rs, (filled / filled.shift(freq="5D") - 1).reindex_like(filled)
@@ -84,10 +69,12 @@ def test_pct_change(self, 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})
 
-        chg = df.pct_change()
+        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])
         edf = DataFrame({"a": expected, "b": expected})
         tm.assert_frame_equal(chg, edf)
@@ -106,31 +93,18 @@ def test_pct_change_shift_over_nas(self):
     def test_pct_change_periods_freq(
         self, datetime_frame, freq, periods, fill_method, limit
     ):
-        msg = (
-            "The 'fill_method' and 'limit' keywords 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, fill_method=fill_method, limit=limit
+        )
+        rs_periods = datetime_frame.pct_change(
+            periods, fill_method=fill_method, limit=limit
+        )
         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, fill_method=fill_method, limit=limit)
+        rs_periods = empty_ts.pct_change(periods, fill_method=fill_method, limit=limit)
         tm.assert_frame_equal(rs_freq, rs_periods)
 
 
@@ -140,13 +114,7 @@ def test_pct_change_with_duplicated_indices(fill_method):
     data = DataFrame(
         {0: [np.nan, 1, 2, 3, 9, 18], 1: [0, 1, np.nan, 3, 9, 18]}, index=["a", "b"] * 3
     )
-
-    msg = (
-        "The 'fill_method' and 'limit' keywords in "
-        "DataFrame.pct_change are deprecated"
-    )
-    with tm.assert_produces_warning(FutureWarning, match=msg):
-        result = data.pct_change(fill_method=fill_method)
+    result = data.pct_change(fill_method=fill_method)
 
     if fill_method is None:
         second_column = [np.nan, np.inf, np.nan, np.nan, 2.0, 1.0]

From 3cb930b301893ea4f4af0af16118b1b8a1c40bd8 Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Mon, 5 Jun 2023 17:10:53 +0800
Subject: [PATCH 05/13] typo

---
 pandas/core/generic.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 1f5ba8fe0a890..9b6d62fe9e3ca 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -11275,7 +11275,7 @@ def pct_change(
         GOOG  0.179241  0.094112   NaN
         APPL -0.252395 -0.011860   NaN
         """
-        # GH#53491: deprecate default fill_method=False
+        # GH#53491: deprecate default fill_method="pad"
         # TODO: In 3.x, change default fill_method=None, then also in 3.x
         # deprecate the fill_method and limit keywords, and finally remove
         # them in 4.x

From 829f9f96ff4e49775bc4cd0899ce59fef9390c0e Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Mon, 5 Jun 2023 18:48:36 +0800
Subject: [PATCH 06/13] GroupBy pct_change only deprecate default

---
 pandas/core/groupby/groupby.py                | 21 ++---
 .../tests/groupby/transform/test_transform.py | 80 +++++++++++++++----
 2 files changed, 76 insertions(+), 25 deletions(-)

diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index d7d24940a0885..3b4c3b615e235 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -3946,7 +3946,7 @@ def pct_change(
         self,
         periods: int = 1,
         fill_method: FillnaOptions | lib.NoDefault = lib.no_default,
-        limit: int | None | lib.NoDefault = lib.no_default,
+        limit: int | None = None,
         freq=None,
         axis: Axis | lib.NoDefault = lib.no_default,
     ):
@@ -3958,20 +3958,21 @@ def pct_change(
         Series or DataFrame
             Percentage changes within each group.
         """
-        if fill_method is not lib.no_default or limit is not lib.no_default:
-            # GH#53491
+        # GH#53491: deprecate default fill_method="ffill"
+        # TODO: In 3.x, change default fill_method=None, then also in 3.x
+        # deprecate the fill_method and limit keywords, and finally remove
+        # them in 4.x
+        if fill_method is 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 fillna directly before "
-                "calling pct_change instead.",
+                f"The default fill_method='ffill' in {type(self).__name__}.pct_change "
+                "is deprecated and will be changed to None in a future version of "
+                "pandas. Pass fill_method='ffill' to retain current behavior or "
+                "fill_method=None to adopt the future default and silence this "
+                "warning.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
-        if fill_method is lib.no_default:
             fill_method = "ffill"
-        if limit is lib.no_default:
-            limit = None
 
         if axis is not lib.no_default:
             axis = self.obj._get_axis_number(axis)
diff --git a/pandas/tests/groupby/transform/test_transform.py b/pandas/tests/groupby/transform/test_transform.py
index 6f67a5aae03ba..aff03b3654af5 100644
--- a/pandas/tests/groupby/transform/test_transform.py
+++ b/pandas/tests/groupby/transform/test_transform.py
@@ -169,8 +169,18 @@ def test_transform_axis_1(request, transformation_func):
     msg = "DataFrame.groupby with axis=1 is deprecated"
     with tm.assert_produces_warning(FutureWarning, match=msg):
         gb = df.groupby([0, 0, 1], axis=1)
-    result = gb.transform(transformation_func, *args)
-    expected = df.T.groupby([0, 0, 1]).transform(transformation_func, *args).T
+
+    pct_change_msg = (
+        "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
+    )
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=pct_change_msg):
+            result = gb.transform("pct_change", *args)
+        with tm.assert_produces_warning(FutureWarning, match=pct_change_msg):
+            expected = df.T.groupby([0, 0, 1]).transform("pct_change", *args).T
+    else:
+        result = gb.transform(transformation_func, *args)
+        expected = df.T.groupby([0, 0, 1]).transform(transformation_func, *args).T
 
     if transformation_func in ["diff", "shift"]:
         # Result contains nans, so transpose coerces to float
@@ -404,11 +414,25 @@ def mock_op(x):
         test_op = lambda x: x.transform(transformation_func)
         mock_op = lambda x: getattr(x, transformation_func)()
 
-    result = test_op(df.groupby("A"))
+    msg = "The default fill_method='pad' in DataFrame.pct_change is deprecated"
+    groupby_msg = (
+        "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
+    )
+
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=groupby_msg):
+            result = test_op(df.groupby("A"))
+    else:
+        result = test_op(df.groupby("A"))
+
     # pass the group in same order as iterating `for ... in df.groupby(...)`
     # but reorder to match df's index since this is a transform
     groups = [df[["B"]].iloc[4:6], df[["B"]].iloc[6:], df[["B"]].iloc[:4]]
-    expected = concat([mock_op(g) for g in groups]).sort_index()
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            expected = concat([mock_op(g) for g in groups]).sort_index()
+    else:
+        expected = concat([mock_op(g) for g in groups]).sort_index()
     # sort_index does not preserve the freq
     expected = expected.set_axis(df.index)
 
@@ -969,14 +993,9 @@ def test_pct_change(frame_or_series, freq, periods, fill_method, limit):
     else:
         expected = expected.to_frame("vals")
 
-    msg = (
-        "The 'fill_method' and 'limit' keywords in "
-        f"{type(gb).__name__}.pct_change are deprecated"
+    result = gb.pct_change(
+        periods=periods, fill_method=fill_method, limit=limit, freq=freq
     )
-    with tm.assert_produces_warning(FutureWarning, match=msg):
-        result = gb.pct_change(
-            periods=periods, fill_method=fill_method, limit=limit, freq=freq
-        )
     tm.assert_equal(result, expected)
 
 
@@ -1394,6 +1413,11 @@ def test_null_group_str_transformer(request, dropna, transformation_func):
     args = get_groupby_method_args(transformation_func, df)
     gb = df.groupby("A", dropna=dropna)
 
+    msg = "The default fill_method='pad' in DataFrame.pct_change is deprecated"
+    groupby_msg = (
+        "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
+    )
+
     buffer = []
     for k, (idx, group) in enumerate(gb):
         if transformation_func == "cumcount":
@@ -1401,6 +1425,9 @@ def test_null_group_str_transformer(request, dropna, transformation_func):
             res = DataFrame({"B": range(len(group))}, index=group.index)
         elif transformation_func == "ngroup":
             res = DataFrame(len(group) * [k], index=group.index, columns=["B"])
+        elif transformation_func == "pct_change":
+            with tm.assert_produces_warning(FutureWarning, match=msg):
+                res = getattr(group[["B"]], "pct_change")(*args)
         else:
             res = getattr(group[["B"]], transformation_func)(*args)
         buffer.append(res)
@@ -1413,7 +1440,11 @@ def test_null_group_str_transformer(request, dropna, transformation_func):
         # ngroup/cumcount always returns a Series as it counts the groups, not values
         expected = expected["B"].rename(None)
 
-    result = gb.transform(transformation_func, *args)
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=groupby_msg):
+            result = gb.transform("pct_change", *args)
+    else:
+        result = gb.transform(transformation_func, *args)
 
     tm.assert_equal(result, expected)
 
@@ -1465,6 +1496,11 @@ def test_null_group_str_transformer_series(dropna, transformation_func):
     args = get_groupby_method_args(transformation_func, ser)
     gb = ser.groupby([1, 1, np.nan], dropna=dropna)
 
+    msg = "The default fill_method='pad' in Series.pct_change is deprecated"
+    groupby_msg = (
+        "The default fill_method='ffill' in SeriesGroupBy.pct_change is deprecated"
+    )
+
     buffer = []
     for k, (idx, group) in enumerate(gb):
         if transformation_func == "cumcount":
@@ -1472,6 +1508,9 @@ def test_null_group_str_transformer_series(dropna, transformation_func):
             res = Series(range(len(group)), index=group.index)
         elif transformation_func == "ngroup":
             res = Series(k, index=group.index)
+        elif transformation_func == "pct_change":
+            with tm.assert_produces_warning(FutureWarning, match=msg):
+                res = getattr(group, "pct_change")(*args)
         else:
             res = getattr(group, transformation_func)(*args)
         buffer.append(res)
@@ -1480,7 +1519,10 @@ def test_null_group_str_transformer_series(dropna, transformation_func):
         buffer.append(Series([np.nan], index=[3], dtype=dtype))
     expected = concat(buffer)
 
-    with tm.assert_produces_warning(None):
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=groupby_msg):
+            result = gb.transform("pct_change", *args)
+    else:
         result = gb.transform(transformation_func, *args)
 
     tm.assert_equal(result, expected)
@@ -1523,6 +1565,14 @@ def test_as_index_no_change(keys, df, groupby_func):
     args = get_groupby_method_args(groupby_func, df)
     gb_as_index_true = df.groupby(keys, as_index=True)
     gb_as_index_false = df.groupby(keys, as_index=False)
-    result = gb_as_index_true.transform(groupby_func, *args)
-    expected = gb_as_index_false.transform(groupby_func, *args)
+
+    msg = "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
+    if groupby_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            result = gb_as_index_true.transform("pct_change", *args)
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            expected = gb_as_index_false.transform("pct_change", *args)
+    else:
+        result = gb_as_index_true.transform(groupby_func, *args)
+        expected = gb_as_index_false.transform(groupby_func, *args)
     tm.assert_equal(result, expected)

From 959ee5d5b69a8b9e098351c89f67d6af3eca05cf Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Mon, 5 Jun 2023 18:52:44 +0800
Subject: [PATCH 07/13] changelod updated correspondingly

---
 doc/source/whatsnew/v2.1.0.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v2.1.0.rst b/doc/source/whatsnew/v2.1.0.rst
index b97d5ea7ce1f4..e15a8bfd82c92 100644
--- a/doc/source/whatsnew/v2.1.0.rst
+++ b/doc/source/whatsnew/v2.1.0.rst
@@ -223,7 +223,6 @@ Other API changes
 Deprecations
 ~~~~~~~~~~~~
 - Deprecated 'broadcast_axis' keyword in :meth:`Series.align` and :meth:`DataFrame.align`, upcast before calling ``align`` with ``left = DataFrame({col: left for col in right.columns}, index=right.index)`` (:issue:`51856`)
-- Deprecated 'fill_method' and 'limit' keywords in :meth:`DataFrame.pct_change`, :meth:`Series.pct_change`, :meth:`DataFrameGroupBy.pct_change`, and :meth:`SeriesGroupBy.pct_change`, explicitly call ``fillna`` before calling ``pct_change`` instead (:issue:`53491`)
 - Deprecated 'method', 'limit', and 'fill_axis' keywords in :meth:`DataFrame.align` and :meth:`Series.align`, explicitly call ``fillna`` on the alignment results instead (:issue:`51856`)
 - Deprecated 'quantile' keyword in :meth:`Rolling.quantile` and :meth:`Expanding.quantile`, renamed as 'q' instead (:issue:`52550`)
 - Deprecated :meth:`.DataFrameGroupBy.apply` and methods on the objects returned by :meth:`.DataFrameGroupBy.resample` operating on the grouping column(s); select the columns to operate on after groupby to either explicitly include or exclude the groupings and avoid the ``FutureWarning`` (:issue:`7155`)
@@ -240,6 +239,7 @@ Deprecations
 - Deprecated the ``axis`` keyword in :meth:`DataFrame.ewm`, :meth:`Series.ewm`, :meth:`DataFrame.rolling`, :meth:`Series.rolling`, :meth:`DataFrame.expanding`, :meth:`Series.expanding` (:issue:`51778`)
 - Deprecated the ``axis`` keyword in :meth:`DataFrame.resample`, :meth:`Series.resample` (:issue:`51778`)
 - Deprecated the behavior of :func:`concat` with both ``len(keys) != len(objs)``, in a future version this will raise instead of truncating to the shorter of the two sequences (:issue:`43485`)
+- Deprecated the default of ``fill_method="pad"`` in :meth:`DataFrame.pct_change` and :meth:`Series.pct_change`, and ``fill_method="ffill"`` in :meth:`DataFrameGroupBy.pct_change` and :meth:`SeriesGroupBy.pct_change`; these will all default to ``None`` in a future version (:issue:`53491`)
 - Deprecated the default of ``observed=False`` in :meth:`DataFrame.groupby` and :meth:`Series.groupby`; this will default to ``True`` in a future version (:issue:`43999`)
 - Deprecating pinning ``group.name`` to each group in :meth:`SeriesGroupBy.aggregate` aggregations; if your operation requires utilizing the groupby keys, iterate over the groupby object instead (:issue:`41090`)
 - Deprecated the 'axis' keyword in :meth:`.GroupBy.idxmax`, :meth:`.GroupBy.idxmin`, :meth:`.GroupBy.fillna`, :meth:`.GroupBy.take`, :meth:`.GroupBy.skew`, :meth:`.GroupBy.rank`, :meth:`.GroupBy.cumprod`, :meth:`.GroupBy.cumsum`, :meth:`.GroupBy.cummax`, :meth:`.GroupBy.cummin`, :meth:`.GroupBy.pct_change`, :meth:`GroupBy.diff`, :meth:`.GroupBy.shift`, and :meth:`DataFrameGroupBy.corrwith`; for ``axis=1`` operate on the underlying :class:`DataFrame` instead (:issue:`50405`, :issue:`51046`)

From 2cb449bab9ede4440d01d8158c9d6b44ecc4632e Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Thu, 8 Jun 2023 00:22:32 +0800
Subject: [PATCH 08/13] reverting

---
 pandas/core/generic.py                        | 21 ++---
 pandas/core/groupby/groupby.py                | 21 ++---
 pandas/tests/frame/methods/test_pct_change.py | 78 ++++++------------
 .../tests/groupby/transform/test_transform.py | 80 +++++++++++++++----
 4 files changed, 110 insertions(+), 90 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 0704cf3d1dae1..9b6d62fe9e3ca 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -11144,7 +11144,7 @@ def pct_change(
         self,
         periods: int = 1,
         fill_method: FillnaOptions | None | lib.NoDefault = lib.no_default,
-        limit: int | None | lib.NoDefault = lib.no_default,
+        limit: int | None = None,
         freq=None,
         **kwargs,
     ) -> Self:
@@ -11275,20 +11275,21 @@ def pct_change(
         GOOG  0.179241  0.094112   NaN
         APPL -0.252395 -0.011860   NaN
         """
-        if fill_method is not lib.no_default or limit is not lib.no_default:
-            # GH#53491
+        # GH#53491: deprecate default fill_method="pad"
+        # TODO: In 3.x, change default fill_method=None, then also in 3.x
+        # deprecate the fill_method and limit keywords, and finally remove
+        # them in 4.x
+        if fill_method is 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 fillna directly before "
-                "calling pct_change instead.",
+                f"The default fill_method='pad' in {type(self).__name__}.pct_change "
+                "is deprecated and will be changed to None in a future version of "
+                "pandas. Pass fill_method='pad' to retain current behavior or "
+                "fill_method=None to adopt the future default and silence this "
+                "warning.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
-        if fill_method is lib.no_default:
             fill_method = "pad"
-        if limit is lib.no_default:
-            limit = None
 
         axis = self._get_axis_number(kwargs.pop("axis", "index"))
         if fill_method is None:
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index d7d24940a0885..3b4c3b615e235 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -3946,7 +3946,7 @@ def pct_change(
         self,
         periods: int = 1,
         fill_method: FillnaOptions | lib.NoDefault = lib.no_default,
-        limit: int | None | lib.NoDefault = lib.no_default,
+        limit: int | None = None,
         freq=None,
         axis: Axis | lib.NoDefault = lib.no_default,
     ):
@@ -3958,20 +3958,21 @@ def pct_change(
         Series or DataFrame
             Percentage changes within each group.
         """
-        if fill_method is not lib.no_default or limit is not lib.no_default:
-            # GH#53491
+        # GH#53491: deprecate default fill_method="ffill"
+        # TODO: In 3.x, change default fill_method=None, then also in 3.x
+        # deprecate the fill_method and limit keywords, and finally remove
+        # them in 4.x
+        if fill_method is 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 fillna directly before "
-                "calling pct_change instead.",
+                f"The default fill_method='ffill' in {type(self).__name__}.pct_change "
+                "is deprecated and will be changed to None in a future version of "
+                "pandas. Pass fill_method='ffill' to retain current behavior or "
+                "fill_method=None to adopt the future default and silence this "
+                "warning.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
-        if fill_method is lib.no_default:
             fill_method = "ffill"
-        if limit is lib.no_default:
-            limit = None
 
         if axis is not lib.no_default:
             axis = self.obj._get_axis_number(axis)
diff --git a/pandas/tests/frame/methods/test_pct_change.py b/pandas/tests/frame/methods/test_pct_change.py
index d53631e75587d..9ad61693ee608 100644
--- a/pandas/tests/frame/methods/test_pct_change.py
+++ b/pandas/tests/frame/methods/test_pct_change.py
@@ -10,7 +10,7 @@
 
 class TestDataFramePctChange:
     @pytest.mark.parametrize(
-        "periods, fill_method, limit, exp",
+        "periods,fill_method,limit,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]),
@@ -28,12 +28,7 @@ def test_pct_change_with_nas(
         vals = [np.nan, np.nan, 1, 2, 4, 10, np.nan, np.nan]
         obj = frame_or_series(vals)
 
-        msg = (
-            "The 'fill_method' and 'limit' keywords 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, fill_method=fill_method, limit=limit)
         tm.assert_equal(res, frame_or_series(exp))
 
     def test_pct_change_numeric(self):
@@ -45,38 +40,28 @@ def test_pct_change_numeric(self):
         pnl.iat[1, 1] = np.nan
         pnl.iat[2, 3] = 60
 
-        msg = (
-            "The 'fill_method' and 'limit' keywords 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")
+            result = pnl.pct_change(axis=axis, fill_method="pad")
             tm.assert_frame_equal(result, expected)
 
     def test_pct_change(self, datetime_frame):
-        msg = (
-            "The 'fill_method' and 'limit' keywords in "
-            "DataFrame.pct_change are deprecated"
-        )
+        msg = "The default fill_method='pad' in DataFrame.pct_change is 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)
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rs = datetime_frame.pct_change(2)
         filled = datetime_frame.fillna(method="pad")
         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)
+        rs = datetime_frame.pct_change(fill_method="bfill", limit=1)
         filled = datetime_frame.fillna(method="bfill", limit=1)
         tm.assert_frame_equal(rs, filled / filled.shift(1) - 1)
 
-        rs = datetime_frame.pct_change(freq="5D")
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rs = datetime_frame.pct_change(freq="5D")
         filled = datetime_frame.fillna(method="pad")
         tm.assert_frame_equal(
             rs, (filled / filled.shift(freq="5D") - 1).reindex_like(filled)
@@ -84,10 +69,12 @@ def test_pct_change(self, 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})
 
-        chg = df.pct_change()
+        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])
         edf = DataFrame({"a": expected, "b": expected})
         tm.assert_frame_equal(chg, edf)
@@ -106,31 +93,18 @@ def test_pct_change_shift_over_nas(self):
     def test_pct_change_periods_freq(
         self, datetime_frame, freq, periods, fill_method, limit
     ):
-        msg = (
-            "The 'fill_method' and 'limit' keywords 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, fill_method=fill_method, limit=limit
+        )
+        rs_periods = datetime_frame.pct_change(
+            periods, fill_method=fill_method, limit=limit
+        )
         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, fill_method=fill_method, limit=limit)
+        rs_periods = empty_ts.pct_change(periods, fill_method=fill_method, limit=limit)
         tm.assert_frame_equal(rs_freq, rs_periods)
 
 
@@ -140,13 +114,7 @@ def test_pct_change_with_duplicated_indices(fill_method):
     data = DataFrame(
         {0: [np.nan, 1, 2, 3, 9, 18], 1: [0, 1, np.nan, 3, 9, 18]}, index=["a", "b"] * 3
     )
-
-    msg = (
-        "The 'fill_method' and 'limit' keywords in "
-        "DataFrame.pct_change are deprecated"
-    )
-    with tm.assert_produces_warning(FutureWarning, match=msg):
-        result = data.pct_change(fill_method=fill_method)
+    result = data.pct_change(fill_method=fill_method)
 
     if fill_method is None:
         second_column = [np.nan, np.inf, np.nan, np.nan, 2.0, 1.0]
diff --git a/pandas/tests/groupby/transform/test_transform.py b/pandas/tests/groupby/transform/test_transform.py
index 6f67a5aae03ba..aff03b3654af5 100644
--- a/pandas/tests/groupby/transform/test_transform.py
+++ b/pandas/tests/groupby/transform/test_transform.py
@@ -169,8 +169,18 @@ def test_transform_axis_1(request, transformation_func):
     msg = "DataFrame.groupby with axis=1 is deprecated"
     with tm.assert_produces_warning(FutureWarning, match=msg):
         gb = df.groupby([0, 0, 1], axis=1)
-    result = gb.transform(transformation_func, *args)
-    expected = df.T.groupby([0, 0, 1]).transform(transformation_func, *args).T
+
+    pct_change_msg = (
+        "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
+    )
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=pct_change_msg):
+            result = gb.transform("pct_change", *args)
+        with tm.assert_produces_warning(FutureWarning, match=pct_change_msg):
+            expected = df.T.groupby([0, 0, 1]).transform("pct_change", *args).T
+    else:
+        result = gb.transform(transformation_func, *args)
+        expected = df.T.groupby([0, 0, 1]).transform(transformation_func, *args).T
 
     if transformation_func in ["diff", "shift"]:
         # Result contains nans, so transpose coerces to float
@@ -404,11 +414,25 @@ def mock_op(x):
         test_op = lambda x: x.transform(transformation_func)
         mock_op = lambda x: getattr(x, transformation_func)()
 
-    result = test_op(df.groupby("A"))
+    msg = "The default fill_method='pad' in DataFrame.pct_change is deprecated"
+    groupby_msg = (
+        "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
+    )
+
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=groupby_msg):
+            result = test_op(df.groupby("A"))
+    else:
+        result = test_op(df.groupby("A"))
+
     # pass the group in same order as iterating `for ... in df.groupby(...)`
     # but reorder to match df's index since this is a transform
     groups = [df[["B"]].iloc[4:6], df[["B"]].iloc[6:], df[["B"]].iloc[:4]]
-    expected = concat([mock_op(g) for g in groups]).sort_index()
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            expected = concat([mock_op(g) for g in groups]).sort_index()
+    else:
+        expected = concat([mock_op(g) for g in groups]).sort_index()
     # sort_index does not preserve the freq
     expected = expected.set_axis(df.index)
 
@@ -969,14 +993,9 @@ def test_pct_change(frame_or_series, freq, periods, fill_method, limit):
     else:
         expected = expected.to_frame("vals")
 
-    msg = (
-        "The 'fill_method' and 'limit' keywords in "
-        f"{type(gb).__name__}.pct_change are deprecated"
+    result = gb.pct_change(
+        periods=periods, fill_method=fill_method, limit=limit, freq=freq
     )
-    with tm.assert_produces_warning(FutureWarning, match=msg):
-        result = gb.pct_change(
-            periods=periods, fill_method=fill_method, limit=limit, freq=freq
-        )
     tm.assert_equal(result, expected)
 
 
@@ -1394,6 +1413,11 @@ def test_null_group_str_transformer(request, dropna, transformation_func):
     args = get_groupby_method_args(transformation_func, df)
     gb = df.groupby("A", dropna=dropna)
 
+    msg = "The default fill_method='pad' in DataFrame.pct_change is deprecated"
+    groupby_msg = (
+        "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
+    )
+
     buffer = []
     for k, (idx, group) in enumerate(gb):
         if transformation_func == "cumcount":
@@ -1401,6 +1425,9 @@ def test_null_group_str_transformer(request, dropna, transformation_func):
             res = DataFrame({"B": range(len(group))}, index=group.index)
         elif transformation_func == "ngroup":
             res = DataFrame(len(group) * [k], index=group.index, columns=["B"])
+        elif transformation_func == "pct_change":
+            with tm.assert_produces_warning(FutureWarning, match=msg):
+                res = getattr(group[["B"]], "pct_change")(*args)
         else:
             res = getattr(group[["B"]], transformation_func)(*args)
         buffer.append(res)
@@ -1413,7 +1440,11 @@ def test_null_group_str_transformer(request, dropna, transformation_func):
         # ngroup/cumcount always returns a Series as it counts the groups, not values
         expected = expected["B"].rename(None)
 
-    result = gb.transform(transformation_func, *args)
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=groupby_msg):
+            result = gb.transform("pct_change", *args)
+    else:
+        result = gb.transform(transformation_func, *args)
 
     tm.assert_equal(result, expected)
 
@@ -1465,6 +1496,11 @@ def test_null_group_str_transformer_series(dropna, transformation_func):
     args = get_groupby_method_args(transformation_func, ser)
     gb = ser.groupby([1, 1, np.nan], dropna=dropna)
 
+    msg = "The default fill_method='pad' in Series.pct_change is deprecated"
+    groupby_msg = (
+        "The default fill_method='ffill' in SeriesGroupBy.pct_change is deprecated"
+    )
+
     buffer = []
     for k, (idx, group) in enumerate(gb):
         if transformation_func == "cumcount":
@@ -1472,6 +1508,9 @@ def test_null_group_str_transformer_series(dropna, transformation_func):
             res = Series(range(len(group)), index=group.index)
         elif transformation_func == "ngroup":
             res = Series(k, index=group.index)
+        elif transformation_func == "pct_change":
+            with tm.assert_produces_warning(FutureWarning, match=msg):
+                res = getattr(group, "pct_change")(*args)
         else:
             res = getattr(group, transformation_func)(*args)
         buffer.append(res)
@@ -1480,7 +1519,10 @@ def test_null_group_str_transformer_series(dropna, transformation_func):
         buffer.append(Series([np.nan], index=[3], dtype=dtype))
     expected = concat(buffer)
 
-    with tm.assert_produces_warning(None):
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=groupby_msg):
+            result = gb.transform("pct_change", *args)
+    else:
         result = gb.transform(transformation_func, *args)
 
     tm.assert_equal(result, expected)
@@ -1523,6 +1565,14 @@ def test_as_index_no_change(keys, df, groupby_func):
     args = get_groupby_method_args(groupby_func, df)
     gb_as_index_true = df.groupby(keys, as_index=True)
     gb_as_index_false = df.groupby(keys, as_index=False)
-    result = gb_as_index_true.transform(groupby_func, *args)
-    expected = gb_as_index_false.transform(groupby_func, *args)
+
+    msg = "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
+    if groupby_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            result = gb_as_index_true.transform("pct_change", *args)
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            expected = gb_as_index_false.transform("pct_change", *args)
+    else:
+        result = gb_as_index_true.transform(groupby_func, *args)
+        expected = gb_as_index_false.transform(groupby_func, *args)
     tm.assert_equal(result, expected)

From 446569458dcff158f8fb804c03a6d0ebfbb152fc Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Thu, 8 Jun 2023 00:30:28 +0800
Subject: [PATCH 09/13] Revert "reverting"

This reverts commit 2cb449bab9ede4440d01d8158c9d6b44ecc4632e.
---
 pandas/core/generic.py                        | 21 +++--
 pandas/core/groupby/groupby.py                | 21 +++--
 pandas/tests/frame/methods/test_pct_change.py | 78 ++++++++++++------
 .../tests/groupby/transform/test_transform.py | 80 ++++---------------
 4 files changed, 90 insertions(+), 110 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 9b6d62fe9e3ca..0704cf3d1dae1 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -11144,7 +11144,7 @@ def pct_change(
         self,
         periods: int = 1,
         fill_method: FillnaOptions | None | lib.NoDefault = lib.no_default,
-        limit: int | None = None,
+        limit: int | None | lib.NoDefault = lib.no_default,
         freq=None,
         **kwargs,
     ) -> Self:
@@ -11275,21 +11275,20 @@ def pct_change(
         GOOG  0.179241  0.094112   NaN
         APPL -0.252395 -0.011860   NaN
         """
-        # GH#53491: deprecate default fill_method="pad"
-        # TODO: In 3.x, change default fill_method=None, then also in 3.x
-        # deprecate the fill_method and limit keywords, and finally remove
-        # them in 4.x
-        if fill_method is lib.no_default:
+        if fill_method is not lib.no_default or limit is not lib.no_default:
+            # GH#53491
             warnings.warn(
-                f"The default fill_method='pad' in {type(self).__name__}.pct_change "
-                "is deprecated and will be changed to None in a future version of "
-                "pandas. Pass fill_method='pad' to retain current behavior or "
-                "fill_method=None to adopt the future default and silence this "
-                "warning.",
+                "The 'fill_method' and 'limit' keywords in "
+                f"{type(self).__name__}.pct_change are deprecated and will be "
+                "removed in a future version. Call fillna directly before "
+                "calling pct_change instead.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
+        if fill_method is lib.no_default:
             fill_method = "pad"
+        if limit is lib.no_default:
+            limit = None
 
         axis = self._get_axis_number(kwargs.pop("axis", "index"))
         if fill_method is None:
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 3b4c3b615e235..d7d24940a0885 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -3946,7 +3946,7 @@ def pct_change(
         self,
         periods: int = 1,
         fill_method: FillnaOptions | lib.NoDefault = lib.no_default,
-        limit: int | None = None,
+        limit: int | None | lib.NoDefault = lib.no_default,
         freq=None,
         axis: Axis | lib.NoDefault = lib.no_default,
     ):
@@ -3958,21 +3958,20 @@ def pct_change(
         Series or DataFrame
             Percentage changes within each group.
         """
-        # GH#53491: deprecate default fill_method="ffill"
-        # TODO: In 3.x, change default fill_method=None, then also in 3.x
-        # deprecate the fill_method and limit keywords, and finally remove
-        # them in 4.x
-        if fill_method is lib.no_default:
+        if fill_method is not lib.no_default or limit is not lib.no_default:
+            # GH#53491
             warnings.warn(
-                f"The default fill_method='ffill' in {type(self).__name__}.pct_change "
-                "is deprecated and will be changed to None in a future version of "
-                "pandas. Pass fill_method='ffill' to retain current behavior or "
-                "fill_method=None to adopt the future default and silence this "
-                "warning.",
+                "The 'fill_method' and 'limit' keywords in "
+                f"{type(self).__name__}.pct_change are deprecated and will be "
+                "removed in a future version. Call fillna directly before "
+                "calling pct_change instead.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
+        if fill_method is lib.no_default:
             fill_method = "ffill"
+        if limit is lib.no_default:
+            limit = None
 
         if axis is not lib.no_default:
             axis = self.obj._get_axis_number(axis)
diff --git a/pandas/tests/frame/methods/test_pct_change.py b/pandas/tests/frame/methods/test_pct_change.py
index 9ad61693ee608..d53631e75587d 100644
--- a/pandas/tests/frame/methods/test_pct_change.py
+++ b/pandas/tests/frame/methods/test_pct_change.py
@@ -10,7 +10,7 @@
 
 class TestDataFramePctChange:
     @pytest.mark.parametrize(
-        "periods,fill_method,limit,exp",
+        "periods, fill_method, limit, 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]),
@@ -28,7 +28,12 @@ def test_pct_change_with_nas(
         vals = [np.nan, np.nan, 1, 2, 4, 10, np.nan, np.nan]
         obj = frame_or_series(vals)
 
-        res = obj.pct_change(periods=periods, fill_method=fill_method, limit=limit)
+        msg = (
+            "The 'fill_method' and 'limit' keywords 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)
         tm.assert_equal(res, frame_or_series(exp))
 
     def test_pct_change_numeric(self):
@@ -40,28 +45,38 @@ def test_pct_change_numeric(self):
         pnl.iat[1, 1] = np.nan
         pnl.iat[2, 3] = 60
 
+        msg = (
+            "The 'fill_method' and 'limit' keywords in "
+            "DataFrame.pct_change are deprecated"
+        )
+
         for axis in range(2):
             expected = pnl.ffill(axis=axis) / pnl.ffill(axis=axis).shift(axis=axis) - 1
-            result = pnl.pct_change(axis=axis, fill_method="pad")
+
+            with tm.assert_produces_warning(FutureWarning, match=msg):
+                result = pnl.pct_change(axis=axis, fill_method="pad")
             tm.assert_frame_equal(result, expected)
 
     def test_pct_change(self, datetime_frame):
-        msg = "The default fill_method='pad' in DataFrame.pct_change is deprecated"
+        msg = (
+            "The 'fill_method' and 'limit' keywords in "
+            "DataFrame.pct_change are deprecated"
+        )
 
-        rs = datetime_frame.pct_change(fill_method=None)
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rs = datetime_frame.pct_change(fill_method=None)
         tm.assert_frame_equal(rs, datetime_frame / datetime_frame.shift(1) - 1)
 
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            rs = datetime_frame.pct_change(2)
+        rs = datetime_frame.pct_change(2)
         filled = datetime_frame.fillna(method="pad")
         tm.assert_frame_equal(rs, filled / filled.shift(2) - 1)
 
-        rs = datetime_frame.pct_change(fill_method="bfill", limit=1)
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rs = datetime_frame.pct_change(fill_method="bfill", limit=1)
         filled = datetime_frame.fillna(method="bfill", limit=1)
         tm.assert_frame_equal(rs, filled / filled.shift(1) - 1)
 
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            rs = datetime_frame.pct_change(freq="5D")
+        rs = datetime_frame.pct_change(freq="5D")
         filled = datetime_frame.fillna(method="pad")
         tm.assert_frame_equal(
             rs, (filled / filled.shift(freq="5D") - 1).reindex_like(filled)
@@ -69,12 +84,10 @@ def test_pct_change(self, 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()
+        df = DataFrame({"a": s, "b": s})
 
+        chg = df.pct_change()
         expected = Series([np.nan, 0.5, 0.0, 2.5 / 1.5 - 1, 0.2])
         edf = DataFrame({"a": expected, "b": expected})
         tm.assert_frame_equal(chg, edf)
@@ -93,18 +106,31 @@ def test_pct_change_shift_over_nas(self):
     def test_pct_change_periods_freq(
         self, datetime_frame, freq, periods, fill_method, limit
     ):
-        # GH#7292
-        rs_freq = datetime_frame.pct_change(
-            freq=freq, fill_method=fill_method, limit=limit
-        )
-        rs_periods = datetime_frame.pct_change(
-            periods, fill_method=fill_method, limit=limit
+        msg = (
+            "The 'fill_method' and 'limit' keywords 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
+            )
         tm.assert_frame_equal(rs_freq, rs_periods)
 
         empty_ts = DataFrame(index=datetime_frame.index, columns=datetime_frame.columns)
-        rs_freq = empty_ts.pct_change(freq=freq, fill_method=fill_method, limit=limit)
-        rs_periods = empty_ts.pct_change(periods, fill_method=fill_method, limit=limit)
+        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
+            )
         tm.assert_frame_equal(rs_freq, rs_periods)
 
 
@@ -114,7 +140,13 @@ def test_pct_change_with_duplicated_indices(fill_method):
     data = DataFrame(
         {0: [np.nan, 1, 2, 3, 9, 18], 1: [0, 1, np.nan, 3, 9, 18]}, index=["a", "b"] * 3
     )
-    result = data.pct_change(fill_method=fill_method)
+
+    msg = (
+        "The 'fill_method' and 'limit' keywords in "
+        "DataFrame.pct_change are deprecated"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = data.pct_change(fill_method=fill_method)
 
     if fill_method is None:
         second_column = [np.nan, np.inf, np.nan, np.nan, 2.0, 1.0]
diff --git a/pandas/tests/groupby/transform/test_transform.py b/pandas/tests/groupby/transform/test_transform.py
index aff03b3654af5..6f67a5aae03ba 100644
--- a/pandas/tests/groupby/transform/test_transform.py
+++ b/pandas/tests/groupby/transform/test_transform.py
@@ -169,18 +169,8 @@ def test_transform_axis_1(request, transformation_func):
     msg = "DataFrame.groupby with axis=1 is deprecated"
     with tm.assert_produces_warning(FutureWarning, match=msg):
         gb = df.groupby([0, 0, 1], axis=1)
-
-    pct_change_msg = (
-        "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
-    )
-    if transformation_func == "pct_change":
-        with tm.assert_produces_warning(FutureWarning, match=pct_change_msg):
-            result = gb.transform("pct_change", *args)
-        with tm.assert_produces_warning(FutureWarning, match=pct_change_msg):
-            expected = df.T.groupby([0, 0, 1]).transform("pct_change", *args).T
-    else:
-        result = gb.transform(transformation_func, *args)
-        expected = df.T.groupby([0, 0, 1]).transform(transformation_func, *args).T
+    result = gb.transform(transformation_func, *args)
+    expected = df.T.groupby([0, 0, 1]).transform(transformation_func, *args).T
 
     if transformation_func in ["diff", "shift"]:
         # Result contains nans, so transpose coerces to float
@@ -414,25 +404,11 @@ def mock_op(x):
         test_op = lambda x: x.transform(transformation_func)
         mock_op = lambda x: getattr(x, transformation_func)()
 
-    msg = "The default fill_method='pad' in DataFrame.pct_change is deprecated"
-    groupby_msg = (
-        "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
-    )
-
-    if transformation_func == "pct_change":
-        with tm.assert_produces_warning(FutureWarning, match=groupby_msg):
-            result = test_op(df.groupby("A"))
-    else:
-        result = test_op(df.groupby("A"))
-
+    result = test_op(df.groupby("A"))
     # pass the group in same order as iterating `for ... in df.groupby(...)`
     # but reorder to match df's index since this is a transform
     groups = [df[["B"]].iloc[4:6], df[["B"]].iloc[6:], df[["B"]].iloc[:4]]
-    if transformation_func == "pct_change":
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            expected = concat([mock_op(g) for g in groups]).sort_index()
-    else:
-        expected = concat([mock_op(g) for g in groups]).sort_index()
+    expected = concat([mock_op(g) for g in groups]).sort_index()
     # sort_index does not preserve the freq
     expected = expected.set_axis(df.index)
 
@@ -993,9 +969,14 @@ def test_pct_change(frame_or_series, freq, periods, fill_method, limit):
     else:
         expected = expected.to_frame("vals")
 
-    result = gb.pct_change(
-        periods=periods, fill_method=fill_method, limit=limit, freq=freq
+    msg = (
+        "The 'fill_method' and 'limit' keywords in "
+        f"{type(gb).__name__}.pct_change are deprecated"
     )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = gb.pct_change(
+            periods=periods, fill_method=fill_method, limit=limit, freq=freq
+        )
     tm.assert_equal(result, expected)
 
 
@@ -1413,11 +1394,6 @@ def test_null_group_str_transformer(request, dropna, transformation_func):
     args = get_groupby_method_args(transformation_func, df)
     gb = df.groupby("A", dropna=dropna)
 
-    msg = "The default fill_method='pad' in DataFrame.pct_change is deprecated"
-    groupby_msg = (
-        "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
-    )
-
     buffer = []
     for k, (idx, group) in enumerate(gb):
         if transformation_func == "cumcount":
@@ -1425,9 +1401,6 @@ def test_null_group_str_transformer(request, dropna, transformation_func):
             res = DataFrame({"B": range(len(group))}, index=group.index)
         elif transformation_func == "ngroup":
             res = DataFrame(len(group) * [k], index=group.index, columns=["B"])
-        elif transformation_func == "pct_change":
-            with tm.assert_produces_warning(FutureWarning, match=msg):
-                res = getattr(group[["B"]], "pct_change")(*args)
         else:
             res = getattr(group[["B"]], transformation_func)(*args)
         buffer.append(res)
@@ -1440,11 +1413,7 @@ def test_null_group_str_transformer(request, dropna, transformation_func):
         # ngroup/cumcount always returns a Series as it counts the groups, not values
         expected = expected["B"].rename(None)
 
-    if transformation_func == "pct_change":
-        with tm.assert_produces_warning(FutureWarning, match=groupby_msg):
-            result = gb.transform("pct_change", *args)
-    else:
-        result = gb.transform(transformation_func, *args)
+    result = gb.transform(transformation_func, *args)
 
     tm.assert_equal(result, expected)
 
@@ -1496,11 +1465,6 @@ def test_null_group_str_transformer_series(dropna, transformation_func):
     args = get_groupby_method_args(transformation_func, ser)
     gb = ser.groupby([1, 1, np.nan], dropna=dropna)
 
-    msg = "The default fill_method='pad' in Series.pct_change is deprecated"
-    groupby_msg = (
-        "The default fill_method='ffill' in SeriesGroupBy.pct_change is deprecated"
-    )
-
     buffer = []
     for k, (idx, group) in enumerate(gb):
         if transformation_func == "cumcount":
@@ -1508,9 +1472,6 @@ def test_null_group_str_transformer_series(dropna, transformation_func):
             res = Series(range(len(group)), index=group.index)
         elif transformation_func == "ngroup":
             res = Series(k, index=group.index)
-        elif transformation_func == "pct_change":
-            with tm.assert_produces_warning(FutureWarning, match=msg):
-                res = getattr(group, "pct_change")(*args)
         else:
             res = getattr(group, transformation_func)(*args)
         buffer.append(res)
@@ -1519,10 +1480,7 @@ def test_null_group_str_transformer_series(dropna, transformation_func):
         buffer.append(Series([np.nan], index=[3], dtype=dtype))
     expected = concat(buffer)
 
-    if transformation_func == "pct_change":
-        with tm.assert_produces_warning(FutureWarning, match=groupby_msg):
-            result = gb.transform("pct_change", *args)
-    else:
+    with tm.assert_produces_warning(None):
         result = gb.transform(transformation_func, *args)
 
     tm.assert_equal(result, expected)
@@ -1565,14 +1523,6 @@ def test_as_index_no_change(keys, df, groupby_func):
     args = get_groupby_method_args(groupby_func, df)
     gb_as_index_true = df.groupby(keys, as_index=True)
     gb_as_index_false = df.groupby(keys, as_index=False)
-
-    msg = "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
-    if groupby_func == "pct_change":
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            result = gb_as_index_true.transform("pct_change", *args)
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            expected = gb_as_index_false.transform("pct_change", *args)
-    else:
-        result = gb_as_index_true.transform(groupby_func, *args)
-        expected = gb_as_index_false.transform(groupby_func, *args)
+    result = gb_as_index_true.transform(groupby_func, *args)
+    expected = gb_as_index_false.transform(groupby_func, *args)
     tm.assert_equal(result, expected)

From f87392b40fe0b09b97a83d18c03faf7cc40bf6e0 Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Thu, 8 Jun 2023 01:45:04 +0800
Subject: [PATCH 10/13] resolved conversation: also warn if nan and not
 specified

---
 pandas/core/generic.py                        | 16 ++++++++++---
 pandas/core/groupby/groupby.py                | 16 ++++++++++---
 pandas/tests/frame/methods/test_pct_change.py |  5 +++-
 .../tests/groupby/transform/test_transform.py | 24 ++++++++++++++++---
 .../tests/series/methods/test_pct_change.py   |  5 +++-
 5 files changed, 55 insertions(+), 11 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 0704cf3d1dae1..2c05d4d7a67ef 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -11275,17 +11275,27 @@ def pct_change(
         GOOG  0.179241  0.094112   NaN
         APPL -0.252395 -0.011860   NaN
         """
+        # GH#53491
         if fill_method is not lib.no_default or limit is not lib.no_default:
-            # GH#53491
             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 fillna directly before "
-                "calling pct_change instead.",
+                "removed in a future version. Call fillna before calling pct_change "
+                "instead.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
         if fill_method is lib.no_default:
+            if self.isna().values.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 fillna with method='ffill' "
+                    "before calling pct_change to retain current behavior and "
+                    "and silence this warning.",
+                    FutureWarning,
+                    stacklevel=find_stack_level(),
+                )
             fill_method = "pad"
         if limit is lib.no_default:
             limit = None
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index d7d24940a0885..1566fb04b7464 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -3958,17 +3958,27 @@ def pct_change(
         Series or DataFrame
             Percentage changes within each group.
         """
+        # GH#53491
         if fill_method is not lib.no_default or limit is not lib.no_default:
-            # GH#53491
             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 fillna directly before "
-                "calling pct_change instead.",
+                "removed in a future version. Call fillna before calling pct_change "
+                "instead.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
         if fill_method is lib.no_default:
+            if 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 fillna with method='ffill' "
+                    "before calling pct_change to retain current behavior and "
+                    "silence this warning.",
+                    FutureWarning,
+                    stacklevel=find_stack_level(),
+                )
             fill_method = "ffill"
         if limit is lib.no_default:
             limit = None
diff --git a/pandas/tests/frame/methods/test_pct_change.py b/pandas/tests/frame/methods/test_pct_change.py
index d53631e75587d..e07d01b0d2f95 100644
--- a/pandas/tests/frame/methods/test_pct_change.py
+++ b/pandas/tests/frame/methods/test_pct_change.py
@@ -87,7 +87,10 @@ def test_pct_change_shift_over_nas(self):
 
         df = DataFrame({"a": s, "b": s})
 
-        chg = df.pct_change()
+        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])
         edf = DataFrame({"a": expected, "b": expected})
         tm.assert_frame_equal(chg, edf)
diff --git a/pandas/tests/groupby/transform/test_transform.py b/pandas/tests/groupby/transform/test_transform.py
index 6f67a5aae03ba..1544dfd22b12f 100644
--- a/pandas/tests/groupby/transform/test_transform.py
+++ b/pandas/tests/groupby/transform/test_transform.py
@@ -404,11 +404,24 @@ def mock_op(x):
         test_op = lambda x: x.transform(transformation_func)
         mock_op = lambda x: getattr(x, transformation_func)()
 
-    result = test_op(df.groupby("A"))
+    msg = "The default fill_method='pad' in DataFrame.pct_change is deprecated"
+    groupby_msg = (
+        "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
+    )
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=groupby_msg):
+            result = test_op(df.groupby("A"))
+    else:
+        result = test_op(df.groupby("A"))
+
     # pass the group in same order as iterating `for ... in df.groupby(...)`
     # but reorder to match df's index since this is a transform
     groups = [df[["B"]].iloc[4:6], df[["B"]].iloc[6:], df[["B"]].iloc[:4]]
-    expected = concat([mock_op(g) for g in groups]).sort_index()
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            expected = concat([mock_op(g) for g in groups]).sort_index()
+    else:
+        expected = concat([mock_op(g) for g in groups]).sort_index()
     # sort_index does not preserve the freq
     expected = expected.set_axis(df.index)
 
@@ -1413,7 +1426,12 @@ def test_null_group_str_transformer(request, dropna, transformation_func):
         # ngroup/cumcount always returns a Series as it counts the groups, not values
         expected = expected["B"].rename(None)
 
-    result = gb.transform(transformation_func, *args)
+    msg = "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
+    if transformation_func == "pct_change" and not dropna:
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            result = gb.transform("pct_change", *args)
+    else:
+        result = gb.transform(transformation_func, *args)
 
     tm.assert_equal(result, expected)
 
diff --git a/pandas/tests/series/methods/test_pct_change.py b/pandas/tests/series/methods/test_pct_change.py
index 51447fc0283aa..d149bf87f4726 100644
--- a/pandas/tests/series/methods/test_pct_change.py
+++ b/pandas/tests/series/methods/test_pct_change.py
@@ -47,7 +47,10 @@ def test_pct_change_with_duplicate_axis(self):
     def test_pct_change_shift_over_nas(self):
         s = Series([1.0, 1.5, np.nan, 2.5, 3.0])
 
-        chg = s.pct_change()
+        msg = "The default fill_method='pad' in Series.pct_change is deprecated"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            chg = s.pct_change()
+
         expected = Series([np.nan, 0.5, 0.0, 2.5 / 1.5 - 1, 0.2])
         tm.assert_series_equal(chg, expected)
 

From 375449ec6771ecda054210bd4260707b7289bcfa Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Thu, 8 Jun 2023 11:32:56 +0800
Subject: [PATCH 11/13] modify msgs since fillna method deprecated; tests
 updated

---
 pandas/core/generic.py                      | 10 +++++-----
 pandas/core/groupby/groupby.py              | 10 +++++-----
 pandas/tests/groupby/test_groupby_dropna.py |  9 ++++++++-
 3 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 382b1cc51e3d8..1d2b6e32a08f9 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -11356,8 +11356,9 @@ def pct_change(
             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 fillna before calling pct_change "
-                "instead.",
+                "removed in a future version. Call "
+                f"{'bfill' if fill_method in ('backfill', 'bfill') else 'ffill'} "
+                "before calling pct_change instead.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
@@ -11366,9 +11367,8 @@ def pct_change(
                 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 fillna with method='ffill' "
-                    "before calling pct_change to retain current behavior and "
-                    "and silence this warning.",
+                    "removed in a future version. Call ffill before calling "
+                    "pct_change to retain current behavior and silence this warning.",
                     FutureWarning,
                     stacklevel=find_stack_level(),
                 )
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 845e724ef3087..bbe59f9884aa1 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -4381,8 +4381,9 @@ def pct_change(
             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 fillna before calling pct_change "
-                "instead.",
+                "removed in a future version. Call "
+                f"{'bfill' if fill_method in ('backfill', 'bfill') else 'ffill'} "
+                "before calling pct_change instead.",
                 FutureWarning,
                 stacklevel=find_stack_level(),
             )
@@ -4391,9 +4392,8 @@ def pct_change(
                 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 fillna with method='ffill' "
-                    "before calling pct_change to retain current behavior and "
-                    "silence this warning.",
+                    "removed in a future version. Call ffill before calling "
+                    "pct_change to retain current behavior and silence this warning.",
                     FutureWarning,
                     stacklevel=find_stack_level(),
                 )
diff --git a/pandas/tests/groupby/test_groupby_dropna.py b/pandas/tests/groupby/test_groupby_dropna.py
index 269fda8fbf361..ab268a1d94b96 100644
--- a/pandas/tests/groupby/test_groupby_dropna.py
+++ b/pandas/tests/groupby/test_groupby_dropna.py
@@ -622,8 +622,15 @@ def test_categorical_transformers(
         "x", dropna=False, observed=observed, sort=sort, as_index=as_index
     )
     gb_dropna = df.groupby("x", dropna=True, observed=observed, sort=sort)
-    result = getattr(gb_keepna, transformation_func)(*args)
+
+    msg = "The default fill_method='ffill' in DataFrameGroupBy.pct_change is deprecated"
+    if transformation_func == "pct_change":
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            result = getattr(gb_keepna, "pct_change")(*args)
+    else:
+        result = getattr(gb_keepna, transformation_func)(*args)
     expected = getattr(gb_dropna, transformation_func)(*args)
+
     for iloc, value in zip(
         df[df["x"].isnull()].index.tolist(), null_group_result.values.ravel()
     ):

From 0ca61a5707d2f019e4b21896a36c19d5f123333f Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Thu, 8 Jun 2023 11:35:16 +0800
Subject: [PATCH 12/13] changelog updated

---
 doc/source/whatsnew/v2.1.0.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v2.1.0.rst b/doc/source/whatsnew/v2.1.0.rst
index 3baf06bba7359..91d82d7742c1a 100644
--- a/doc/source/whatsnew/v2.1.0.rst
+++ b/doc/source/whatsnew/v2.1.0.rst
@@ -225,6 +225,7 @@ Other API changes
 Deprecations
 ~~~~~~~~~~~~
 - Deprecated 'broadcast_axis' keyword in :meth:`Series.align` and :meth:`DataFrame.align`, upcast before calling ``align`` with ``left = DataFrame({col: left for col in right.columns}, index=right.index)`` (:issue:`51856`)
+- Deprecated 'fill_method' and 'limit' keywords in :meth:`DataFrame.pct_change`, :meth:`Series.pct_change`, :meth:`DataFrameGroupBy.pct_change`, and :meth:`SeriesGroupBy.pct_change`, explicitly call ``ffill`` or ``bfill`` before calling ``pct_change`` instead (:issue:`53491`)
 - Deprecated 'method', 'limit', and 'fill_axis' keywords in :meth:`DataFrame.align` and :meth:`Series.align`, explicitly call ``fillna`` on the alignment results instead (:issue:`51856`)
 - Deprecated 'quantile' keyword in :meth:`Rolling.quantile` and :meth:`Expanding.quantile`, renamed as 'q' instead (:issue:`52550`)
 - Deprecated :meth:`.DataFrameGroupBy.apply` and methods on the objects returned by :meth:`.DataFrameGroupBy.resample` operating on the grouping column(s); select the columns to operate on after groupby to either explicitly include or exclude the groupings and avoid the ``FutureWarning`` (:issue:`7155`)
@@ -243,7 +244,6 @@ Deprecations
 - Deprecated the ``axis`` keyword in :meth:`DataFrame.ewm`, :meth:`Series.ewm`, :meth:`DataFrame.rolling`, :meth:`Series.rolling`, :meth:`DataFrame.expanding`, :meth:`Series.expanding` (:issue:`51778`)
 - Deprecated the ``axis`` keyword in :meth:`DataFrame.resample`, :meth:`Series.resample` (:issue:`51778`)
 - Deprecated the behavior of :func:`concat` with both ``len(keys) != len(objs)``, in a future version this will raise instead of truncating to the shorter of the two sequences (:issue:`43485`)
-- Deprecated the default of ``fill_method="pad"`` in :meth:`DataFrame.pct_change` and :meth:`Series.pct_change`, and ``fill_method="ffill"`` in :meth:`DataFrameGroupBy.pct_change` and :meth:`SeriesGroupBy.pct_change`; these will all default to ``None`` in a future version (:issue:`53491`)
 - Deprecated the default of ``observed=False`` in :meth:`DataFrame.groupby` and :meth:`Series.groupby`; this will default to ``True`` in a future version (:issue:`43999`)
 - Deprecating pinning ``group.name`` to each group in :meth:`SeriesGroupBy.aggregate` aggregations; if your operation requires utilizing the groupby keys, iterate over the groupby object instead (:issue:`41090`)
 - Deprecated the 'axis' keyword in :meth:`.GroupBy.idxmax`, :meth:`.GroupBy.idxmin`, :meth:`.GroupBy.fillna`, :meth:`.GroupBy.take`, :meth:`.GroupBy.skew`, :meth:`.GroupBy.rank`, :meth:`.GroupBy.cumprod`, :meth:`.GroupBy.cumsum`, :meth:`.GroupBy.cummax`, :meth:`.GroupBy.cummin`, :meth:`.GroupBy.pct_change`, :meth:`GroupBy.diff`, :meth:`.GroupBy.shift`, and :meth:`DataFrameGroupBy.corrwith`; for ``axis=1`` operate on the underlying :class:`DataFrame` instead (:issue:`50405`, :issue:`51046`)

From c4b6732e410aea5602ec8ac463a64783c640bc37 Mon Sep 17 00:00:00 2001
From: Charlie-XIAO <yx2436@nyu.edu>
Date: Thu, 8 Jun 2023 13:55:32 +0800
Subject: [PATCH 13/13] docstring use ffill instead of fillna

---
 pandas/core/generic.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 1d2b6e32a08f9..f73ef36f76086 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -11304,7 +11304,7 @@ def pct_change(
         3    85.0
         dtype: float64
 
-        >>> s.fillna(method='ffill').pct_change()
+        >>> s.ffill().pct_change()
         0         NaN
         1    0.011111
         2    0.000000