BUG: DataFrame slice selection treated as hashable in Python 3.12 #57500

doc/source/whatsnew/v3.0.0.rst

@@ -340,6 +340,7 @@ Bug fixes
 ~~~~~~~~~
 - Fixed bug in :class:`SparseDtype` for equal comparison with na fill value. (:issue:`54770`)
 - Fixed bug in :meth:`.DataFrameGroupBy.median` where nat values gave an incorrect result. (:issue:`57926`)
+- Fixed bug in :meth:`DataFrame.__getitem__` returning modified columns when called with ``slice`` on Python 3.12 (:issue:`57500`)
 - Fixed bug in :meth:`DataFrame.cumsum` which was raising ``IndexError`` if dtype is ``timedelta64[ns]`` (:issue:`57956`)
 - Fixed bug in :meth:`DataFrame.eval` and :meth:`DataFrame.query` which caused an exception when using NumPy attributes via ``@`` notation, e.g., ``df.eval("@np.floor(a)")``. (:issue:`58041`)
 - Fixed bug in :meth:`DataFrame.join` inconsistently setting result index name (:issue:`55815`)
@@ -352,6 +353,7 @@ Bug fixes
 - Fixed bug in :meth:`Series.replace` and :meth:`DataFrame.replace` inconsistently replacing matching instances when ``regex=True`` and missing values are present. (:issue:`56599`)
 - Fixed bug in :meth:`read_csv` raising ``TypeError`` when ``index_col`` is specified and ``na_values`` is a dict containing the key ``None``. (:issue:`57547`)
 
+
 Categorical
 ^^^^^^^^^^^
 -

pandas/core/frame.py

@@ -3855,8 +3855,10 @@ def __getitem__(self, key):
         key = lib.item_from_zerodim(key)
         key = com.apply_if_callable(key, self)
 
-        if is_hashable(key) and not is_iterator(key):
+        if is_hashable(key) and not is_iterator(key) and not isinstance(key, slice):
             # is_iterator to exclude generator e.g. test_getitem_listlike
+            # As of Python 3.12, slice is hashable which breaks MultiIndex (GH#57500)
+
             # shortcut if the key is in columns
             is_mi = isinstance(self.columns, MultiIndex)
             # GH#45316 Return view if key is not duplicated

pandas/tests/frame/indexing/test_indexing.py

@@ -524,6 +524,16 @@ def test_loc_setitem_boolean_mask_allfalse(self):
         result.loc[result.b.isna(), "a"] = result.a.copy()
         tm.assert_frame_equal(result, df)
 
+    def test_getitem_slice_empty(self):
+        df = DataFrame([[1]], columns=MultiIndex.from_product([["A"], ["a"]]))
+        result = df[:]
+
+        expected = DataFrame([[1]], columns=MultiIndex.from_product([["A"], ["a"]]))
+
+        tm.assert_frame_equal(result, expected)
+        # Ensure df[:] returns a view of df, not the same object
+        assert result is not df
+
     def test_getitem_fancy_slice_integers_step(self):
         df = DataFrame(np.random.default_rng(2).standard_normal((10, 5)))