gh-130167: Improve speed of difflib.IS_LINE_JUNK by replacing re

Lib/difflib.py

@@ -1038,11 +1038,9 @@ def _qformat(self, aline, bline, atags, btags):
 # remaining is that perhaps it was really the case that " volatile"
 # was inserted after "private".  I can live with that <wink>.
 
-import re
-
-def IS_LINE_JUNK(line, pat=re.compile(r"\s*(?:#\s*)?$").match):
+def IS_LINE_JUNK(line, pat=None):
     r"""
-    Return True for ignorable line: iff `line` is blank or contains a single '#'.
+    Return True for ignorable line: if `line` is blank or contains a single '#'.
 
     Examples:
 
@@ -1054,6 +1052,8 @@ def IS_LINE_JUNK(line, pat=re.compile(r"\s*(?:#\s*)?$").match):
     False
     """
 
+    if pat is None:
+        return line.strip() in ('', '#')
     return pat(line) is not None
 
 def IS_CHARACTER_JUNK(ch, ws=" \t"):
@@ -2027,7 +2027,6 @@ def make_table(self,fromlines,tolines,fromdesc='',todesc='',context=False,
                      replace('\1','</span>'). \
                      replace('\t','&nbsp;')
 
-del re
 
 def restore(delta, which):
     r"""

Misc/NEWS.d/next/Library/2025-02-16-06-25-01.gh-issue-130167.kUg7Rc.rst

@@ -0,0 +1,2 @@
+Improve speed of :func:`difflib.IS_LINE_JUNK` by replacing :mod:`re` with
+built-in string methods.