From 13d70ff1fed0114330f300cf1de9c4b9f143f278 Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Sun, 21 Feb 2021 11:31:30 +0100
Subject: [PATCH 1/3] performance improvement by limiting .join()

---
 pandas/io/formats/templates/html.tpl | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/pandas/io/formats/templates/html.tpl b/pandas/io/formats/templates/html.tpl
index b315c57a65cdf..a595538fb0af6 100644
--- a/pandas/io/formats/templates/html.tpl
+++ b/pandas/io/formats/templates/html.tpl
@@ -56,7 +56,11 @@
     <tr>
 {% for c in r %}
 {% if c.is_visible != False %}
-      <{{c.type}} {% if c.id is defined -%} id="T_{{uuid}}{{c.id}}" {%- endif %} class="{{c.class}}" {{c.attributes|join(" ")}}>{{c.display_value}}</{{c.type}}>
+{% if c.type == 'th' %}
+      <th {% if c.id is defined -%} id="T_{{uuid}}{{c.id}}" {%- endif %} class="{{c.class}}" {{c.attributes|join(" ")}}>{{c.display_value}}</th>
+{% else %}
+      <td {% if c.id is defined -%} id="T_{{uuid}}{{c.id}}" {%- endif %} class="{{c.class}}" >{{c.display_value}}</td>
+{% endif %}
 {% endif %}
 {% endfor %}
     </tr>

From 0b8ad47989c32fd44c32047f19090ca3f3be2a90 Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Sun, 21 Feb 2021 12:24:08 +0100
Subject: [PATCH 2/3] performance improvement by limiting .join()

---
 pandas/io/formats/style.py           | 5 +++--
 pandas/io/formats/templates/html.tpl | 8 ++------
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/pandas/io/formats/style.py b/pandas/io/formats/style.py
index 877e146fd8681..be748dfbdb2d6 100644
--- a/pandas/io/formats/style.py
+++ b/pandas/io/formats/style.py
@@ -466,7 +466,7 @@ def _translate(self):
                     }
                     colspan = col_lengths.get((r, c), 0)
                     if colspan > 1:
-                        es["attributes"] = [f'colspan="{colspan}"']
+                        es["attributes"] = f'colspan="{colspan}"'
                     row_es.append(es)
                 head.append(row_es)
 
@@ -517,7 +517,7 @@ def _translate(self):
                 }
                 rowspan = idx_lengths.get((c, r), 0)
                 if rowspan > 1:
-                    es["attributes"] = [f'rowspan="{rowspan}"']
+                    es["attributes"] = f'rowspan="{rowspan}"'
                 row_es.append(es)
 
             for c, col in enumerate(self.data.columns):
@@ -529,6 +529,7 @@ def _translate(self):
                     "value": value,
                     "display_value": formatter(value),
                     "is_visible": (c not in hidden_columns),
+                    "attributes": "",
                 }
 
                 # only add an id if the cell has a style
diff --git a/pandas/io/formats/templates/html.tpl b/pandas/io/formats/templates/html.tpl
index a595538fb0af6..65fc1dfbb37c4 100644
--- a/pandas/io/formats/templates/html.tpl
+++ b/pandas/io/formats/templates/html.tpl
@@ -39,7 +39,7 @@
     <tr>
 {% for c in r %}
 {% if c.is_visible != False %}
-      <{{c.type}} class="{{c.class}}" {{c.attributes|join(" ")}}>{{c.value}}</{{c.type}}>
+      <{{c.type}} class="{{c.class}}" {{c.attributes}}>{{c.value}}</{{c.type}}>
 {% endif %}
 {% endfor %}
     </tr>
@@ -56,11 +56,7 @@
     <tr>
 {% for c in r %}
 {% if c.is_visible != False %}
-{% if c.type == 'th' %}
-      <th {% if c.id is defined -%} id="T_{{uuid}}{{c.id}}" {%- endif %} class="{{c.class}}" {{c.attributes|join(" ")}}>{{c.display_value}}</th>
-{% else %}
-      <td {% if c.id is defined -%} id="T_{{uuid}}{{c.id}}" {%- endif %} class="{{c.class}}" >{{c.display_value}}</td>
-{% endif %}
+      <{{c.type}} {% if c.id is defined -%} id="T_{{uuid}}{{c.id}}" {%- endif %} class="{{c.class}}" {{c.attributes}}>{{c.display_value}}</{{c.type}}>
 {% endif %}
 {% endfor %}
     </tr>

From b5248115ff76007ed204bf9072b8dcfab94e1e59 Mon Sep 17 00:00:00 2001
From: "JHM Darbyshire (iMac)" <attack68@users.noreply.github.com>
Date: Sun, 21 Feb 2021 12:29:15 +0100
Subject: [PATCH 3/3] fix test

---
 pandas/tests/io/formats/test_style.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/tests/io/formats/test_style.py b/pandas/tests/io/formats/test_style.py
index d134f33e15525..2a6505a43b80a 100644
--- a/pandas/tests/io/formats/test_style.py
+++ b/pandas/tests/io/formats/test_style.py
@@ -1323,7 +1323,7 @@ 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",
         }