BUG: Styler Index when rendering an empty df (#43327)

Author: attack68

doc/source/whatsnew/v1.4.0.rst

@@ -381,7 +381,7 @@ Styler
 - Bug in :meth:`.Styler.to_html` where the ``Styler`` object was updated if the ``to_html`` method was called with some args (:issue:`43034`)
 - Bug in :meth:`.Styler.copy` where ``uuid`` was not previously copied (:issue:`40675`)
 - Bug in :meth:`Styler.apply` where functions which returned Series objects were not correctly handled in terms of aligning their index labels (:issue:`13657`, :issue:`42014`)
--
+- Bug when rendering an empty DataFrame with a named index (:issue:`43305`).
 
 Other
 ^^^^^

pandas/io/formats/style_render.py

@@ -393,7 +393,9 @@ def _translate_header(
                 for c, name in enumerate(self.data.index.names)
             ]
 
-            if len(self.data.columns) <= max_cols:
+            if not clabels:
+                blank_len = 0
+            elif len(self.data.columns) <= max_cols:
                 blank_len = len(clabels[0])
             else:
                 blank_len = len(clabels[0]) + 1  # to allow room for `...` trim col

pandas/tests/io/formats/style/test_style.py

@@ -1,5 +1,6 @@
 import copy
 import re
+from textwrap import dedent
 
 import numpy as np
 import pytest
@@ -187,6 +188,23 @@ def test_render_trimming_mi():
     assert {"attributes": 'colspan="2"'}.items() <= ctx["head"][0][2].items()
 
 
+def test_render_empty_mi():
+    # GH 43305
+    df = DataFrame(index=MultiIndex.from_product([["A"], [0, 1]], names=[None, "one"]))
+    expected = dedent(
+        """\
+    >
+      <thead>
+        <tr>
+          <th class="index_name level0" >&nbsp;</th>
+          <th class="index_name level1" >one</th>
+        </tr>
+      </thead>
+    """
+    )
+    assert expected in df.style.to_html()
+
+
 @pytest.mark.parametrize("comprehensive", [True, False])
 @pytest.mark.parametrize("render", [True, False])
 @pytest.mark.parametrize("deepcopy", [True, False])