DEP: Deprecated pad/backfill for Series/DataFrame (#51221)

Author: phofl

doc/source/whatsnew/v2.0.0.rst

@@ -786,6 +786,10 @@ Deprecations
 - Deprecated calling ``float`` or ``int`` on a single element :class:`Series` to return a ``float`` or ``int`` respectively. Extract the element before calling ``float`` or ``int`` instead (:issue:`51101`)
 - Deprecated :meth:`Grouper.groups`, use :meth:`Groupby.groups` instead (:issue:`51182`)
 - Deprecated :meth:`Grouper.grouper`, use :meth:`Groupby.grouper` instead (:issue:`51182`)
+- Deprecated :meth:`Series.pad` in favor of :meth:`Series.ffill` (:issue:`33396`)
+- Deprecated :meth:`Series.backfill` in favor of :meth:`Series.bfill` (:issue:`33396`)
+- Deprecated :meth:`DataFrame.pad` in favor of :meth:`DataFrame.ffill` (:issue:`33396`)
+- Deprecated :meth:`DataFrame.backfill` in favor of :meth:`DataFrame.bfill` (:issue:`33396`)
 -
 
 .. ---------------------------------------------------------------------------

pandas/core/generic.py

@@ -7001,7 +7001,34 @@ def ffill(
             method="ffill", axis=axis, inplace=inplace, limit=limit, downcast=downcast
         )
 
-    pad = ffill
+    @doc(klass=_shared_doc_kwargs["klass"])
+    def pad(
+        self: NDFrameT,
+        *,
+        axis: None | Axis = None,
+        inplace: bool_t = False,
+        limit: None | int = None,
+        downcast: dict | None = None,
+    ) -> NDFrameT | None:
+        """
+        Synonym for :meth:`DataFrame.fillna` with ``method='ffill'``.
+
+        .. deprecated:: 2.0
+
+            {klass}.pad is deprecated. Use {klass}.ffill instead.
+
+        Returns
+        -------
+        {klass} or None
+            Object with missing values filled or None if ``inplace=True``.
+        """
+        warnings.warn(
+            "DataFrame.pad/Series.pad is deprecated. Use "
+            "DataFrame.ffill/Series.ffill instead",
+            FutureWarning,
+            stacklevel=find_stack_level(),
+        )
+        return self.ffill(axis=axis, inplace=inplace, limit=limit, downcast=downcast)
 
     @overload
     def bfill(
@@ -7057,7 +7084,34 @@ def bfill(
             method="bfill", axis=axis, inplace=inplace, limit=limit, downcast=downcast
         )
 
-    backfill = bfill
+    @doc(klass=_shared_doc_kwargs["klass"])
+    def backfill(
+        self: NDFrameT,
+        *,
+        axis: None | Axis = None,
+        inplace: bool_t = False,
+        limit: None | int = None,
+        downcast: dict | None = None,
+    ) -> NDFrameT | None:
+        """
+        Synonym for :meth:`DataFrame.fillna` with ``method='bfill'``.
+
+        .. deprecated:: 2.0
+
+            {klass}.backfill is deprecated. Use {klass}.backfill instead.
+
+        Returns
+        -------
+        {klass} or None
+            Object with missing values filled or None if ``inplace=True``.
+        """
+        warnings.warn(
+            "DataFrame.backfill/Series.backfill is deprecated. Use "
+            "DataFrame.bfill/Series.bfill instead",
+            FutureWarning,
+            stacklevel=find_stack_level(),
+        )
+        return self.bfill(axis=axis, inplace=inplace, limit=limit, downcast=downcast)
 
     @overload
     def replace(

pandas/tests/frame/methods/test_fillna.py

@@ -769,3 +769,11 @@ def test_fillna_nones_inplace():
 
     expected = DataFrame([[1, 2], [1, 2]], columns=["A", "B"])
     tm.assert_frame_equal(df, expected)
+
+
+@pytest.mark.parametrize("func", ["pad", "backfill"])
+def test_pad_backfill_deprecated(func):
+    # GH#33396
+    df = DataFrame({"a": [1, 2, 3]})
+    with tm.assert_produces_warning(FutureWarning):
+        getattr(df, func)()

pandas/tests/series/methods/test_fillna.py

@@ -970,3 +970,10 @@ def test_fillna_parr(self):
         filled = ser.fillna(method="pad")
 
         tm.assert_series_equal(filled, expected)
+
+    @pytest.mark.parametrize("func", ["pad", "backfill"])
+    def test_pad_backfill_deprecated(self, func):
+        # GH#33396
+        ser = Series([1, 2, 3])
+        with tm.assert_produces_warning(FutureWarning):
+            getattr(ser, func)()