DEPR: fillna method kwd

pandas/conftest.py

@@ -150,6 +150,14 @@ def pytest_collection_modifyitems(items, config) -> None:
             "first is deprecated and will be removed in a future version. "
             "Please create a mask and filter using `.loc` instead",
         ),
+        (
+            "Resampler.fillna",
+            "DatetimeIndexResampler.fillna is deprecated",
+        ),
+        (
+            "DataFrameGroupBy.fillna",
+            "DataFrameGroupBy.fillna with 'method' is deprecated",
+        ),
     ]
 
     for item in items:

pandas/core/generic.py

@@ -7217,6 +7217,13 @@ def ffill(
         2  3.0  4.0 NaN  1.0
         3  3.0  3.0 NaN  4.0
 
+        >>> ser = pd.Series([1, np.NaN, 2, 3])
+        >>> ser.ffill()
+        0   1.0
+        1   1.0
+        2   2.0
+        3   3.0
+        dtype: float64
         """
         self._deprecate_downcast(downcast)
 

pandas/core/resample.py

@@ -823,14 +823,13 @@ def fillna(self, method, limit: int | None = None):
         2018-01-01 01:30:00  6.0  5
         2018-01-01 02:00:00  6.0  5
         """
-        if method is not None:
-            warnings.warn(
-                f"{type(self).__name__}.fillna with 'method' is deprecated and "
-                "will raise in a future version. Use obj.ffill() or obj.bfill() "
-                "instead.",
-                FutureWarning,
-                stacklevel=find_stack_level(),
-            )
+        warnings.warn(
+            f"{type(self).__name__}.fillna is deprecated and will be removed "
+            "in a future version. Use obj.ffill(), obj.bfill(), "
+            "or obj.neaerest() instead.",
+            FutureWarning,
+            stacklevel=find_stack_level(),
+        )
         return self._upsample(method, limit=limit)
 
     def interpolate(

pandas/tests/resample/test_resample_api.py

@@ -290,7 +290,7 @@ def test_fillna():
     r = ts.resample("s")
 
     expected = r.ffill()
-    msg = "DatetimeIndexResampler.fillna with 'method' is deprecated"
+    msg = "DatetimeIndexResampler.fillna is deprecated"
     with tm.assert_produces_warning(FutureWarning, match=msg):
         result = r.fillna(method="ffill")
     tm.assert_series_equal(result, expected)