DEPR: deprecated nonkeyword arguments in to_html

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_html` except ``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_markdown` except ``buf``. (:issue:`54229`)

pandas/core/frame.py

@@ -3134,6 +3134,9 @@ def to_html(
     ) -> str:
         ...
 
+    @deprecate_nonkeyword_arguments(
+        version="3.0", allowed_args=["self", "buf"], name="to_html"
+    )
     @Substitution(
         header_type="bool",
         header="Whether to print column labels, default True",

pandas/tests/io/formats/test_to_html.py

@@ -978,3 +978,14 @@ def test_to_html_empty_complex_array():
         "</table>"
     )
     assert result == expected
+
+
+def test_to_html_pos_args_deprecation():
+    # GH-54229
+    df = DataFrame({"a": [1, 2, 3]})
+    msg = (
+        r"Starting with pandas version 3.0 all arguments of to_html except for the "
+        r"argument 'buf' will be keyword-only."
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        df.to_html(None, None)