Fix accessing .columns by an external API

python/cudf/cudf/_lib/utils.pyx

@@ -149,7 +149,9 @@ cpdef generate_pandas_metadata(table, index):
             col
             for col in table._columns
         ],
-        df=table,
+        # It is OKAY to do `.head(0).to_pandas()` because
+        # this method will extract `.columns` metadata only
+        df=table.head(0).to_pandas(),
         column_names=col_names,
         index_levels=index_levels,
         index_descriptors=index_descriptors,

python/cudf/cudf/core/indexed_frame.py

@@ -2872,6 +2872,8 @@ def _slice(self, arg: slice, keep_index: bool = True) -> Self:
             self._column_names,
             None if has_range_index or not keep_index else self._index.names,
         )
+        result._data.label_dtype = self._data.label_dtype
+        result._data.rangeindex = self._data.rangeindex
 
         if keep_index and has_range_index:
             result.index = self.index[start:stop]
@@ -3053,7 +3055,7 @@ def duplicated(self, subset=None, keep="first"):
 
     @_cudf_nvtx_annotate
     def _empty_like(self, keep_index=True) -> Self:
-        return self._from_columns_like_self(
+        result = self._from_columns_like_self(
             libcudf.copying.columns_empty_like(
                 [
                     *(self._index._data.columns if keep_index else ()),
@@ -3063,6 +3065,9 @@ def _empty_like(self, keep_index=True) -> Self:
             self._column_names,
             self._index.names if keep_index else None,
         )
+        result._data.label_dtype = self._data.label_dtype
+        result._data.rangeindex = self._data.rangeindex
+        return result
 
     def _split(self, splits, keep_index=True):
         if self._num_rows == 0:

python/cudf/cudf/tests/test_dataframe.py

@@ -3012,43 +3012,31 @@ def test_series_rename():
 @pytest.mark.parametrize("data_type", dtypes)
 @pytest.mark.parametrize("nelem", [0, 100])
 def test_head_tail(nelem, data_type):
-    def check_index_equality(left, right):
-        assert left.index.equals(right.index)
-
-    def check_values_equality(left, right):
-        if len(left) == 0 and len(right) == 0:
-            return None
-
-        np.testing.assert_array_equal(left.to_pandas(), right.to_pandas())
-
-    def check_frame_series_equality(left, right):
-        check_index_equality(left, right)
-        check_values_equality(left, right)
-
-    gdf = cudf.DataFrame(
+    pdf = pd.DataFrame(
         {
             "a": np.random.randint(0, 1000, nelem).astype(data_type),
             "b": np.random.randint(0, 1000, nelem).astype(data_type),
         }
     )
+    gdf = cudf.from_pandas(pdf)
 
-    check_frame_series_equality(gdf.head(), gdf[:5])
-    check_frame_series_equality(gdf.head(3), gdf[:3])
-    check_frame_series_equality(gdf.head(-2), gdf[:-2])
-    check_frame_series_equality(gdf.head(0), gdf[0:0])
+    assert_eq(gdf.head(), pdf.head())
+    assert_eq(gdf.head(3), pdf.head(3))
+    assert_eq(gdf.head(-2), pdf.head(-2))
+    assert_eq(gdf.head(0), pdf.head(0))
 
-    check_frame_series_equality(gdf["a"].head(), gdf["a"][:5])
-    check_frame_series_equality(gdf["a"].head(3), gdf["a"][:3])
-    check_frame_series_equality(gdf["a"].head(-2), gdf["a"][:-2])
+    assert_eq(gdf["a"].head(), pdf["a"].head())
+    assert_eq(gdf["a"].head(3), pdf["a"].head(3))
+    assert_eq(gdf["a"].head(-2), pdf["a"].head(-2))
 
-    check_frame_series_equality(gdf.tail(), gdf[-5:])
-    check_frame_series_equality(gdf.tail(3), gdf[-3:])
-    check_frame_series_equality(gdf.tail(-2), gdf[2:])
-    check_frame_series_equality(gdf.tail(0), gdf[0:0])
+    assert_eq(gdf.tail(), pdf.tail())
+    assert_eq(gdf.tail(3), pdf.tail(3))
+    assert_eq(gdf.tail(-2), pdf.tail(-2))
+    assert_eq(gdf.tail(0), pdf.tail(0))
 
-    check_frame_series_equality(gdf["a"].tail(), gdf["a"][-5:])
-    check_frame_series_equality(gdf["a"].tail(3), gdf["a"][-3:])
-    check_frame_series_equality(gdf["a"].tail(-2), gdf["a"][2:])
+    assert_eq(gdf["a"].tail(), pdf["a"].tail())
+    assert_eq(gdf["a"].tail(3), pdf["a"].tail(3))
+    assert_eq(gdf["a"].tail(-2), pdf["a"].tail(-2))
 
 
 def test_tail_for_string():
@@ -4328,6 +4316,17 @@ def test_one_row_head():
     assert_eq(head_pdf, head_gdf)
 
 
+@pytest.mark.parametrize("index", [None, [123], ["a", "b"]])
+def test_no_cols_head(index):
+    pdf = pd.DataFrame(index=index)
+    gdf = cudf.from_pandas(pdf)
+
+    head_gdf = gdf.head()
+    head_pdf = pdf.head()
+
+    assert_eq(head_pdf, head_gdf)
+
+
 @pytest.mark.parametrize("dtype", ALL_TYPES)
 @pytest.mark.parametrize(
     "np_dtype,pd_dtype",