gh-95953: use an f-string for difflib _format_line and update news

Author: KatieLG

Lib/difflib.py

@@ -1927,8 +1927,8 @@ def _format_line(self,side,flag,linenum,text):
         # add a class to the td tag if there is a difference on the line
         css_class = ' class="diff_changed" ' if flag else ' '
 
-        return '<td class="diff_header"%s>%s</td><td%snowrap="nowrap">%s</td>' \
-               % (id,linenum,css_class,text)
+        return f'<td class="diff_header"{id}>{linenum}</td>' \
+            + f'<td{css_class}nowrap="nowrap">{text}</td>' 
 
     def _make_prefix(self):
         """Create unique anchor prefixes"""

Misc/NEWS.d/next/Library/2025-09-22-11-19-05.gh-issue-95953.7oLoag.rst

@@ -1,2 +1,2 @@
 A CSS class, ``diff_changed``, was added to the changed lines in the
-``make_table`` output of :class:`difflib.HtmlDiff`.
+``make_table`` output of :class:`difflib.HtmlDiff`. Patch by Katie Gardner.