PERF: only output an html id if a style is applied (pandas-dev#23019)

* PERF: only output an html id if a style is applied

* Add a parameter to Styler constructor

* Use cell_ids instead of all_ids and set default to True

* remove backslash

Author: Moisan

pandas/io/formats/style.py

@@ -64,6 +64,11 @@ class Styler(object):
         a unique identifier to avoid CSS collisions; generated automatically
     caption: str, default None
         caption to attach to the table
+    cell_ids: bool, default True
+        If True, each cell will have an ``id`` attribute in their HTML tag.
+        The ``id`` takes the form ``T_<uuid>_row<num_row>_col<num_col>``
+        where ``<uuid>`` is the unique identifier, ``<num_row>`` is the row
+        number and ``<num_col>`` is the column number.
 
     Attributes
     ----------
@@ -112,7 +117,7 @@ class Styler(object):
     template = env.get_template("html.tpl")
 
     def __init__(self, data, precision=None, table_styles=None, uuid=None,
-                 caption=None, table_attributes=None):
+                 caption=None, table_attributes=None, cell_ids=True):
         self.ctx = defaultdict(list)
         self._todo = []
 
@@ -136,6 +141,7 @@ def __init__(self, data, precision=None, table_styles=None, uuid=None,
         self.table_attributes = table_attributes
         self.hidden_index = False
         self.hidden_columns = []
+        self.cell_ids = cell_ids
 
         # display_funcs maps (row, col) -> formatting function
 
@@ -306,14 +312,16 @@ def format_attr(pair):
                 cs.extend(cell_context.get("data", {}).get(r, {}).get(c, []))
                 formatter = self._display_funcs[(r, c)]
                 value = self.data.iloc[r, c]
-                row_es.append({
-                    "type": "td",
-                    "value": value,
-                    "class": " ".join(cs),
-                    "id": "_".join(cs[1:]),
-                    "display_value": formatter(value),
-                    "is_visible": (c not in hidden_columns)
-                })
+                row_dict = {"type": "td",
+                            "value": value,
+                            "class": " ".join(cs),
+                            "display_value": formatter(value),
+                            "is_visible": (c not in hidden_columns)}
+                # only add an id if the cell has a style
+                if (self.cell_ids or
+                        not(len(ctx[r, c]) == 1 and ctx[r, c][0] == '')):
+                    row_dict["id"] = "_".join(cs[1:])
+                row_es.append(row_dict)
                 props = []
                 for x in ctx[r, c]:
                     # have to handle empty styles like ['']

pandas/io/formats/templates/html.tpl

@@ -50,17 +50,17 @@
 {%- endblock thead %} 
 {%- block tbody %} 
 <tbody> 
-    {%- block before_rows %}{%- endblock before_rows %}
-    {%- for r in body %} 
-    {%- block tr scoped %}
-    <tr> 
-        {%- for c in r %} 
-        {%- if c.is_visible != False %} 
-        <{{ c.type }} id="T_{{ uuid }}{{ c.id }}" class="{{ c.class }}" {{ c.attributes|join(" ") }}>{{ c.display_value }}</{{ c.type }}>
-        {%- endif %} 
-        {%- endfor %} 
-    </tr> 
-    {%- endblock tr %}
+    {% block before_rows %}{% endblock before_rows %}
+    {% for r in body %}
+    {% block tr scoped %}
+    <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 }}>
+        {% endif %}
+        {%- endfor %}
+    </tr>
+    {% endblock tr %}
     {%- endfor %} 
     {%- block after_rows %}{%- endblock after_rows %}
 </tbody>