added deprecate_nonkeyword_arguments to function where

doc/source/whatsnew/v1.3.0.rst

@@ -681,6 +681,7 @@ Deprecations
 - Deprecated passing arguments as positional (except for ``"method"``) in :meth:`DataFrame.interpolate` and :meth:`Series.interpolate` (:issue:`41485`)
 - Deprecated passing arguments (apart from ``value``) as positional in :meth:`DataFrame.fillna` and :meth:`Series.fillna` (:issue:`41485`)
 - Deprecated construction of :class:`Series` or :class:`DataFrame` with ``DatetimeTZDtype`` data and ``datetime64[ns]`` dtype.  Use ``Series(data).dt.tz_localize(None)`` instead (:issue:`41555`,:issue:`33401`)
+- Deprecated passing arguments as positional in :meth:`DataFrame.where` and :meth:`Series.where` (other than ``"cond"`` and ``"other"``) (:issue:`41485`)
 
 .. _whatsnew_130.deprecations.nuisance_columns:
 

pandas/core/frame.py

@@ -10688,6 +10688,21 @@ def interpolate(
             **kwargs,
         )
 
+    @deprecate_nonkeyword_arguments(
+        version=None, allowed_args=["self", "cond", "other"]
+    )
+    def where(
+        self,
+        cond,
+        other=np.nan,
+        inplace=False,
+        axis=None,
+        level=None,
+        errors="raise",
+        try_cast=lib.no_default,
+    ):
+        return super().where(cond, other, inplace, axis, level, errors, try_cast)
+
 
 DataFrame._add_numeric_operations()
 

pandas/core/generic.py

@@ -9073,7 +9073,6 @@ def _where(
             result = self._constructor(new_data)
             return result.__finalize__(self)
 
-    @final
     @doc(
         klass=_shared_doc_kwargs["klass"],
         cond="True",
@@ -9221,7 +9220,7 @@ def where(
                 "try_cast keyword is deprecated and will be removed in a "
                 "future version",
                 FutureWarning,
-                stacklevel=2,
+                stacklevel=4,
             )
 
         return self._where(cond, other, inplace, axis, level, errors=errors)

pandas/core/series.py

@@ -5310,6 +5310,21 @@ def interpolate(
             **kwargs,
         )
 
+    @deprecate_nonkeyword_arguments(
+        version=None, allowed_args=["self", "cond", "other"]
+    )
+    def where(
+        self,
+        cond,
+        other=np.nan,
+        inplace=False,
+        axis=None,
+        level=None,
+        errors="raise",
+        try_cast=lib.no_default,
+    ):
+        return super().where(cond, other, inplace, axis, level, errors, try_cast)
+
     # ----------------------------------------------------------------------
     # Add index
     _AXIS_ORDERS = ["index"]

pandas/tests/frame/indexing/test_where.py

@@ -757,3 +757,17 @@ def test_where_none_nan_coerce():
     )
     result = expected.where(expected.notnull(), None)
     tm.assert_frame_equal(result, expected)
+
+
+def test_where_non_keyword_deprecation():
+    # GH 41485
+    s = DataFrame(range(5))
+    msg = (
+        "In a future version of pandas all arguments of "
+        "DataFrame.where except for the arguments 'cond' "
+        "and 'other' will be keyword-only"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = s.where(s > 1, 10, False)
+    expected = DataFrame([10, 10, 2, 3, 4])
+    tm.assert_frame_equal(expected, result)

pandas/tests/series/indexing/test_where.py

@@ -141,6 +141,20 @@ def test_where():
     tm.assert_series_equal(rs, expected)
 
 
+def test_where_non_keyword_deprecation():
+    # GH 41485
+    s = Series(range(5))
+    msg = (
+        "In a future version of pandas all arguments of "
+        "Series.where except for the arguments 'cond' "
+        "and 'other' will be keyword-only"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = s.where(s > 1, 10, False)
+    expected = Series([10, 10, 2, 3, 4])
+    tm.assert_series_equal(expected, result)
+
+
 def test_where_error():
     s = Series(np.random.randn(5))
     cond = s > 0