BUG: Ignore warning for duplicate columns in to_dict when orient='tight'

doc/source/whatsnew/v3.0.0.rst

@@ -410,6 +410,7 @@ MultiIndex
 I/O
 ^^^
 - Bug in :class:`DataFrame` and :class:`Series` ``repr`` of :py:class:`collections.abc.Mapping`` elements. (:issue:`57915`)
+- Bug in :meth:`DataFrame.to_dict` raises unnecessary ``UserWarning`` when columns are not unique and ``orient='tight'``. (:issue:`58281`)
 - Bug in :meth:`DataFrame.to_excel` when writing empty :class:`DataFrame` with :class:`MultiIndex` on both axes (:issue:`57696`)
 - Bug in :meth:`DataFrame.to_string` that raised ``StopIteration`` with nested DataFrames. (:issue:`16098`)
 - Bug in :meth:`read_csv` raising ``TypeError`` when ``index_col`` is specified and ``na_values`` is a dict containing the key ``None``. (:issue:`57547`)

pandas/core/methods/to_dict.py

@@ -148,7 +148,7 @@ def to_dict(
  Return a collections.abc.MutableMapping object representing the
  DataFrame. The resulting transformation depends on the `orient` parameter.
  """
- if not df.columns.is_unique:
+ if orient != "tight" and not df.columns.is_unique:
  warnings.warn(
  "DataFrame columns are not unique, some columns will be omitted.",
  UserWarning,

pandas/tests/frame/methods/test_to_dict.py

@@ -513,6 +513,17 @@ def test_to_dict_masked_native_python(self):
  result = df.to_dict(orient="records")
  assert isinstance(result[0]["a"], int)
 
+ def test_to_dict_tight_no_warning_with_duplicate_column(self):
+ # GH#58281
+ df = DataFrame([[1, 2], [3, 4], [5, 6]], columns=["A", "A"])
+ assert df.to_dict(orient="tight") == {
+ "index": [0, 1, 2],
+ "columns": ["A", "A"],
+ "data": [[1, 2], [3, 4], [5, 6]],
+ "index_names": [None],
+ "column_names": [None],
+ }
+
 
 @pytest.mark.parametrize(
  "val", [Timestamp(2020, 1, 1), Timedelta(1), Period("2020"), Interval(1, 2)]