BUG: one level multiindex styler display (#43385)

Author: attack68

doc/source/whatsnew/v1.4.0.rst

@@ -425,6 +425,7 @@ Styler
 - 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`).
+- Bug when rendering a single level MultiIndex (:issue:`43383`).
 
 Other
 ^^^^^

pandas/io/formats/style_render.py

@@ -461,7 +461,7 @@ def _translate_body(
         )
 
         rlabels = self.data.index.tolist()[:max_rows]  # slice to allow trimming
-        if self.data.index.nlevels == 1:
+        if not isinstance(self.data.index, MultiIndex):
             rlabels = [[x] for x in rlabels]
 
         body = []
@@ -896,7 +896,7 @@ def _get_level_lengths(
         hidden_elements = []
 
     lengths = {}
-    if index.nlevels == 1:
+    if not isinstance(index, MultiIndex):
         for i, value in enumerate(levels):
             if i not in hidden_elements:
                 lengths[(0, i)] = 1

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

@@ -4,6 +4,7 @@
 from pandas import (
     DataFrame,
     IndexSlice,
+    MultiIndex,
     NaT,
     Timestamp,
     option_context,
@@ -305,3 +306,14 @@ def test_precision_zero(df):
     ctx = styler._translate(True, True)
     assert ctx["body"][0][2]["display_value"] == "-1"
     assert ctx["body"][1][2]["display_value"] == "-1"
+
+
+def test_1level_multiindex():
+    # GH 43383
+    midx = MultiIndex.from_product([[1, 2]], names=[""])
+    df = DataFrame(-1, index=midx, columns=[0, 1])
+    ctx = df.style._translate(True, True)
+    assert ctx["body"][0][0]["display_value"] == 1
+    assert ctx["body"][0][0]["is_visible"] is True
+    assert ctx["body"][1][0]["display_value"] == 2
+    assert ctx["body"][1][0]["is_visible"] is True