DEPR: deprecated nonkeyword arguments in to_json

doc/source/whatsnew/v2.2.0.rst

@@ -93,6 +93,7 @@ Other API changes
 Deprecations
 ~~~~~~~~~~~~
 - Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_hdf` except ``path_or_buf``. (:issue:`54229`)
+- Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_json` except ``path_or_buf``. (:issue:`54229`)
 - Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_latex` except ``buf``. (:issue:`54229`)
 - Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_pickle` except ``path``. (:issue:`54229`)
 - Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_string` except ``buf``. (:issue:`54229`)

pandas/core/generic.py

@@ -2352,6 +2352,9 @@ def to_excel(
         )
 
     @final
+    @deprecate_nonkeyword_arguments(
+        version="3.0", allowed_args=["self", "path_or_buf"], name="to_json"
+    )
     @doc(
         storage_options=_shared_docs["storage_options"],
         compression_options=_shared_docs["compression_options"] % "path_or_buf",

pandas/tests/io/json/test_pandas.py

@@ -1,7 +1,10 @@
 import datetime
 from datetime import timedelta
 from decimal import Decimal
-from io import StringIO
+from io import (
+    BytesIO,
+    StringIO,
+)
 import json
 import os
 import sys
@@ -2106,3 +2109,15 @@ def test_json_roundtrip_string_inference(orient):
         columns=pd.Index(["col 1", "col 2"], dtype=pd.ArrowDtype(pa.string())),
     )
     tm.assert_frame_equal(result, expected)
+
+
+def test_json_pos_args_deprecation():
+    # GH-54229
+    df = DataFrame({"a": [1, 2, 3]})
+    msg = (
+        r"Starting with pandas version 3.0 all arguments of to_json except for the "
+        r"argument 'path_or_buf' will be keyword-only."
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        buf = BytesIO()
+        df.to_json(buf, "split")