Backport PR #38533: BUG&TST: HTML formatting error in Styler.render() in rowspan attribute (#38640)

Co-authored-by: JoseNavy <[email protected]>

Author: meeseeksmachine

doc/source/whatsnew/v1.2.0.rst

@@ -768,6 +768,10 @@ Plotting
 - Bug in :meth:`DataFrame.plot` and :meth:`Series.plot` was overwriting matplotlib's shared y axes behaviour when no ``sharey`` parameter was passed (:issue:`37942`)
 - Bug in :meth:`DataFrame.plot` was raising a ``TypeError`` with ``ExtensionDtype`` columns (:issue:`32073`)
 
+Styler
+^^^^^^
+
+- Bug in :meth:`Styler.render` HTML was generated incorrectly beacause of formatting error in rowspan attribute, it now matches with w3 syntax. (:issue:`38234`)
 
 Groupby/resample/rolling
 ^^^^^^^^^^^^^^^^^^^^^^^^

pandas/io/formats/style.py

@@ -389,7 +389,7 @@ def format_attr(pair):
                 rowspan = idx_lengths.get((c, r), 0)
                 if rowspan > 1:
                     es["attributes"] = [
-                        format_attr({"key": "rowspan", "value": rowspan})
+                        format_attr({"key": "rowspan", "value": f'"{rowspan}"'})
                     ]
                 row_es.append(es)
 

pandas/tests/io/formats/test_style.py

@@ -1411,7 +1411,7 @@ def test_mi_sparse(self):
             "display_value": "a",
             "is_visible": True,
             "type": "th",
-            "attributes": ["rowspan=2"],
+            "attributes": ['rowspan="2"'],
             "class": "row_heading level0 row0",
             "id": "level0_row0",
         }
@@ -1740,6 +1740,15 @@ def test_colspan_w3(self):
         s = Styler(df, uuid="_", cell_ids=False)
         assert '<th class="col_heading level0 col0" colspan="2">l0</th>' in s.render()
 
+    def test_rowspan_w3(self):
+        # GH 38533
+        df = DataFrame(data=[[1, 2]], index=[["l0", "l0"], ["l1a", "l1b"]])
+        s = Styler(df, uuid="_", cell_ids=False)
+        assert (
+            '<th id="T___level0_row0" class="row_heading '
+            'level0 row0" rowspan="2">l0</th>' in s.render()
+        )
+
     @pytest.mark.parametrize("len_", [1, 5, 32, 33, 100])
     def test_uuid_len(self, len_):
         # GH 36345