ENH: Deprecate non-keyword arguments for Resampler.interpolate

doc/source/whatsnew/v1.3.0.rst

@@ -682,6 +682,7 @@ Deprecations
 - Deprecated passing arguments as positional (except for ``"codes"``) in :meth:`MultiIndex.codes` (:issue:`41485`)
 - Deprecated passing arguments as positional in :meth:`Index.set_names` and :meth:`MultiIndex.set_names` (except for ``names``) (:issue:`41485`)
 - Deprecated passing arguments (apart from ``cond`` and ``other``) as positional in :meth:`DataFrame.mask` and :meth:`Series.mask` (:issue:`41485`)
+- Deprecated passing arguments as positional in :meth:`DataFrame.interpolate` (other than ``"method``) (:issue:`41485`)
 - Deprecated passing arguments as positional in :meth:`DataFrame.clip` and :meth:`Series.clip` (other than ``"upper"`` and ``"lower"``) (:issue:`41485`)
 - Deprecated special treatment of lists with first element a Categorical in the :class:`DataFrame` constructor; pass as ``pd.DataFrame({col: categorical, ...})`` instead (:issue:`38845`)
 - Deprecated passing arguments as positional (except for ``"method"``) in :meth:`DataFrame.interpolate` and :meth:`Series.interpolate` (:issue:`41485`)

pandas/core/resample.py

@@ -35,6 +35,7 @@
     Appender,
     Substitution,
     doc,
+    deprecate_nonkeyword_arguments
 )
 
 from pandas.core.dtypes.generic import (
@@ -832,6 +833,9 @@ def fillna(self, method, limit=None):
         """
         return self._upsample(method, limit=limit)
 
+    @deprecate_nonkeyword_arguments(
+        version=None, allowed_args=["self", "method"]
+    )
     @doc(NDFrame.interpolate, **_shared_docs_kwargs)
     def interpolate(
         self,

pandas/tests/resample/test_deprecated.py

@@ -278,3 +278,19 @@ def test_resample_base_with_timedeltaindex():
 
     tm.assert_index_equal(without_base.index, exp_without_base)
     tm.assert_index_equal(with_base.index, exp_with_base)
+
+
+def test_interpolate_posargs_deprecation():
+
+    df = DataFrame([1.0, np.nan, -2.0, 2.0])
+
+    msg = (
+        r"In a future version of pandas all arguments of DataFrame\.interpolate "
+        r"except for the argument 'method' will be keyword-only"
+    )
+
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = df.interpolate(method='linear', limit_direction='forward', axis=0)
+
+    expected = DataFrame([1.0, -0.5, -2.0, 2.0])
+    tm.assert_frame_equal(result, expected)