allow method to be positional

doc/source/whatsnew/v1.3.0.rst

@@ -647,7 +647,7 @@ Deprecations
 - Deprecated setting :attr:`Categorical._codes`, create a new :class:`Categorical` with the desired codes instead (:issue:`40606`)
 - Deprecated behavior of :meth:`DatetimeIndex.union` with mixed timezones; in a future version both will be cast to UTC instead of object dtype (:issue:`39328`)
 - Deprecated using ``usecols`` with out of bounds indices for ``read_csv`` with ``engine="c"`` (:issue:`25623`)
-- Deprecated passing arguments as positional in :meth:`DataFrame.interpolate` and :meth:`Series.interpolate` (:issue:`41485`)
+- Deprecated passing arguments as positional (except for ``"method"``) in :meth:`DataFrame.interpolate` and :meth:`Series.interpolate` (:issue:`41485`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/generic.py

@@ -6697,7 +6697,7 @@ def replace(
         else:
             return result.__finalize__(self, method="replace")
 
-    @deprecate_nonkeyword_arguments(version="2.0", allowed_args=["self"])
+    @deprecate_nonkeyword_arguments(version="2.0", allowed_args=["self", "method"])
     @final
     def interpolate(
         self: FrameOrSeries,

pandas/tests/frame/methods/test_interpolate.py

@@ -348,7 +348,7 @@ def test_interpolate_pos_args_deprecation(self):
         df = DataFrame({"a": [1, 2, 3]})
         msg = (
             r"Starting with Pandas version 2\.0 all arguments of interpolate except "
-            r"for the argument 'self' will be keyword-only"
+            r"for the arguments 'self' and 'method' will be keyword-only"
         )
         with tm.assert_produces_warning(FutureWarning, match=msg):
-            df.interpolate(0)
+            df.interpolate("pad", 0)

pandas/tests/resample/test_datetime_index.py

@@ -1026,14 +1026,12 @@ def test_resample_dtype_coercion():
     df = {"a": [1, 3, 1, 4]}
     df = DataFrame(df, index=date_range("2017-01-01", "2017-01-04"))
 
-    expected = (
-        df.astype("float64").resample("H").mean()["a"].interpolate(method="cubic")
-    )
+    expected = df.astype("float64").resample("H").mean()["a"].interpolate("cubic")
 
-    result = df.resample("H")["a"].mean().interpolate(method="cubic")
+    result = df.resample("H")["a"].mean().interpolate("cubic")
     tm.assert_series_equal(result, expected)
 
-    result = df.resample("H").mean()["a"].interpolate(method="cubic")
+    result = df.resample("H").mean()["a"].interpolate("cubic")
     tm.assert_series_equal(result, expected)
 
 

pandas/tests/series/methods/test_interpolate.py

@@ -817,7 +817,7 @@ def test_interpolate_pos_args_deprecation(self):
         ser = Series([1, 2, 3])
         msg = (
             r"Starting with Pandas version 2\.0 all arguments of interpolate except "
-            r"for the argument 'self' will be keyword-only"
+            r"for the arguments 'self' and 'method' will be keyword-only"
         )
         with tm.assert_produces_warning(FutureWarning, match=msg):
-            ser.interpolate(0)
+            ser.interpolate("pad", 0)