From 8f2670df73e2d657964fdaffec3eca318014bd4d Mon Sep 17 00:00:00 2001
From: donBarbos <donbarbos@proton.me>
Date: Sun, 16 Feb 2025 06:20:10 +0400
Subject: [PATCH 01/13] Improve speed of difflib.IS_LINE_JUNK by replacing re

---
 Lib/difflib.py                                             | 7 ++-----
 .../Library/2025-02-16-06-25-01.gh-issue-130167.kUg7Rc.rst | 2 ++
 2 files changed, 4 insertions(+), 5 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2025-02-16-06-25-01.gh-issue-130167.kUg7Rc.rst

diff --git a/Lib/difflib.py b/Lib/difflib.py
index c124afdd039559..d12b0d439f27c5 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1038,9 +1038,7 @@ 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):
     r"""
     Return True for ignorable line: iff `line` is blank or contains a single '#'.
 
@@ -1054,7 +1052,7 @@ def IS_LINE_JUNK(line, pat=re.compile(r"\s*(?:#\s*)?$").match):
     False
     """
 
-    return pat(line) is not None
+    return line.strip() == "" or line.lstrip().rstrip() == "#"
 
 def IS_CHARACTER_JUNK(ch, ws=" \t"):
     r"""
@@ -2027,7 +2025,6 @@ def make_table(self,fromlines,tolines,fromdesc='',todesc='',context=False,
                      replace('\1','</span>'). \
                      replace('\t','&nbsp;')
 
-del re
 
 def restore(delta, which):
     r"""
diff --git a/Misc/NEWS.d/next/Library/2025-02-16-06-25-01.gh-issue-130167.kUg7Rc.rst b/Misc/NEWS.d/next/Library/2025-02-16-06-25-01.gh-issue-130167.kUg7Rc.rst
new file mode 100644
index 00000000000000..f58c416930b709
--- /dev/null
+++ b/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.

From 0fae9c52bce2bbe8ed0a1e6128e57f74969af12d Mon Sep 17 00:00:00 2001
From: donBarbos <donbarbos@proton.me>
Date: Sun, 16 Feb 2025 07:20:53 +0400
Subject: [PATCH 02/13] Update difflib.py

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
---
 Lib/difflib.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index d12b0d439f27c5..4ba643c3aec50d 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1038,7 +1038,7 @@ 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>.
 
-def IS_LINE_JUNK(line):
+def IS_LINE_JUNK(line, pat=None):
     r"""
     Return True for ignorable line: iff `line` is blank or contains a single '#'.
 

From 352b4bccc1cf5fa83401c00a115eb2c7e6f47393 Mon Sep 17 00:00:00 2001
From: donBarbos <donbarbos@proton.me>
Date: Sun, 16 Feb 2025 07:21:14 +0400
Subject: [PATCH 03/13] Update difflib.py

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
---
 Lib/difflib.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index 4ba643c3aec50d..e528af5945b63f 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1052,7 +1052,7 @@ def IS_LINE_JUNK(line, pat=None):
     False
     """
 
-    return line.strip() == "" or line.lstrip().rstrip() == "#"
+    return line.strip() in ('', '#')
 
 def IS_CHARACTER_JUNK(ch, ws=" \t"):
     r"""

From 0ab8da87e9e035edb0fb50abb68e1fa2917648e6 Mon Sep 17 00:00:00 2001
From: donBarbos <donbarbos@proton.me>
Date: Sun, 16 Feb 2025 15:51:50 +0400
Subject: [PATCH 04/13] Add backward compatibility

---
 Lib/difflib.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index e528af5945b63f..196c71ed7e2b2c 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1052,7 +1052,9 @@ def IS_LINE_JUNK(line, pat=None):
     False
     """
 
-    return line.strip() in ('', '#')
+    return (line.strip() in ('', '#')
+            if pat is None
+            else pat(line) is not None)
 
 def IS_CHARACTER_JUNK(ch, ws=" \t"):
     r"""

From 64dff4af089707262e4c38a7fb647098f8595d50 Mon Sep 17 00:00:00 2001
From: donBarbos <donbarbos@proton.me>
Date: Sun, 16 Feb 2025 18:42:30 +0400
Subject: [PATCH 05/13] Update difflib.py

---
 Lib/difflib.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index 196c71ed7e2b2c..a665ffecd10a96 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1040,7 +1040,7 @@ def _qformat(self, aline, bline, atags, btags):
 
 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:
 
@@ -1052,9 +1052,9 @@ def IS_LINE_JUNK(line, pat=None):
     False
     """
 
-    return (line.strip() in ('', '#')
-            if pat is None
-            else pat(line) is not None)
+    if pat is None:
+        return line.strip() == '' or line.strip() == '#'
+    return pat(line) is not None
 
 def IS_CHARACTER_JUNK(ch, ws=" \t"):
     r"""

From 32337c3ac65fc313ce8e5b29c194017b21407906 Mon Sep 17 00:00:00 2001
From: donBarbos <donbarbos@proton.me>
Date: Sun, 16 Feb 2025 14:57:46 +0000
Subject: [PATCH 06/13] Update Lib/difflib.py
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 Lib/difflib.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index a665ffecd10a96..7f15acce897c13 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1053,7 +1053,8 @@ def IS_LINE_JUNK(line, pat=None):
     """
 
     if pat is None:
-        return line.strip() == '' or line.strip() == '#'
+        stripped = line.strip()
+        return stripped == '' or stripped == '#'
     return pat(line) is not None
 
 def IS_CHARACTER_JUNK(ch, ws=" \t"):

From 390b6e760a80442bdcc817f81c35b0333c27f02c Mon Sep 17 00:00:00 2001
From: donBarbos <donbarbos@proton.me>
Date: Mon, 17 Feb 2025 11:15:41 +0400
Subject: [PATCH 07/13] Update difflib.py

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
---
 Lib/difflib.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index 7f15acce897c13..2590b7ff9998fb 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1040,7 +1040,7 @@ def _qformat(self, aline, bline, atags, btags):
 
 def IS_LINE_JUNK(line, pat=None):
     r"""
-    Return True for ignorable line: if `line` is blank or contains a single '#'.
+    Return True for ignorable line: if and only if `line` is blank or contains a single '#'.
 
     Examples:
 

From 30d4535f4d2250e3c09be8a1f34f0ceb7e14ed52 Mon Sep 17 00:00:00 2001
From: donBarbos <donbarbos@proton.me>
Date: Tue, 18 Feb 2025 04:19:44 +0400
Subject: [PATCH 08/13] Back `iff` word

---
 Lib/difflib.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index 2590b7ff9998fb..7f15acce897c13 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1040,7 +1040,7 @@ def _qformat(self, aline, bline, atags, btags):
 
 def IS_LINE_JUNK(line, pat=None):
     r"""
-    Return True for ignorable line: if and only if `line` is blank or contains a single '#'.
+    Return True for ignorable line: if `line` is blank or contains a single '#'.
 
     Examples:
 

From 0e7293d752be5d54cca43625b95a6afbefb61176 Mon Sep 17 00:00:00 2001
From: donBarbos <donbarbos@proton.me>
Date: Wed, 19 Feb 2025 00:57:46 +0400
Subject: [PATCH 09/13] Update difflib

---
 Lib/difflib.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index 7f15acce897c13..2d2bb5cf31c2ec 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1053,8 +1053,7 @@ def IS_LINE_JUNK(line, pat=None):
     """
 
     if pat is None:
-        stripped = line.strip()
-        return stripped == '' or stripped == '#'
+        return line.strip() in ('', '#')
     return pat(line) is not None
 
 def IS_CHARACTER_JUNK(ch, ws=" \t"):

From bcf45a36914e911a9b4512f2c408ebec9de0bbca Mon Sep 17 00:00:00 2001
From: donBarbos <donbarbos@proton.me>
Date: Wed, 19 Feb 2025 01:04:59 +0400
Subject: [PATCH 10/13] Update difflib.py

Co-authored-by: Tim Peters <tim.peters@gmail.com>
---
 Lib/difflib.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index 2d2bb5cf31c2ec..c563c683db6a24 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1053,7 +1053,7 @@ def IS_LINE_JUNK(line, pat=None):
     """
 
     if pat is None:
-        return line.strip() in ('', '#')
+        return line.strip() in '#'
     return pat(line) is not None
 
 def IS_CHARACTER_JUNK(ch, ws=" \t"):

From 46a412681eb6d0a7c8bf6546a9ffa2669e01bf06 Mon Sep 17 00:00:00 2001
From: donBarbos <donbarbos@proton.me>
Date: Mon, 28 Apr 2025 01:31:13 +0400
Subject: [PATCH 11/13] Fix News message

---
 .../Library/2025-02-16-06-25-01.gh-issue-130167.kUg7Rc.rst     | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/Misc/NEWS.d/next/Library/2025-02-16-06-25-01.gh-issue-130167.kUg7Rc.rst b/Misc/NEWS.d/next/Library/2025-02-16-06-25-01.gh-issue-130167.kUg7Rc.rst
index f58c416930b709..3d397084fc136c 100644
--- a/Misc/NEWS.d/next/Library/2025-02-16-06-25-01.gh-issue-130167.kUg7Rc.rst
+++ b/Misc/NEWS.d/next/Library/2025-02-16-06-25-01.gh-issue-130167.kUg7Rc.rst
@@ -1,2 +1 @@
-Improve speed of :func:`difflib.IS_LINE_JUNK` by replacing :mod:`re` with
-built-in string methods.
+Improve speed of :func:`difflib.IS_LINE_JUNK`. Patch by Semyon Moroz.

From 60951fb01250ea8f1017e205425866407a215723 Mon Sep 17 00:00:00 2001
From: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
Date: Thu, 1 May 2025 04:41:43 +0100
Subject: [PATCH 12/13] Improve clarity of expression

---
 Lib/difflib.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index c563c683db6a24..6719927682aca8 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1053,7 +1053,7 @@ def IS_LINE_JUNK(line, pat=None):
     """
 
     if pat is None:
-        return line.strip() in '#'
+        return line.strip() in {'', '#'}
     return pat(line) is not None
 
 def IS_CHARACTER_JUNK(ch, ws=" \t"):

From 9d987b466dbc6e6819ecb6c7aace539f0c203ebd Mon Sep 17 00:00:00 2001
From: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
Date: Thu, 1 May 2025 04:46:04 +0100
Subject: [PATCH 13/13] Revert, but add explanatory comments

---
 Lib/difflib.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index 6719927682aca8..f4b453fe77f81b 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -1053,7 +1053,10 @@ def IS_LINE_JUNK(line, pat=None):
     """
 
     if pat is None:
-        return line.strip() in {'', '#'}
+        # Default: match '#' or the empty string
+        return line.strip() in '#'
+   # Previous versions used the undocumented parameter 'pat' as a
+   # match function. Retain this behaviour for compatibility.
     return pat(line) is not None
 
 def IS_CHARACTER_JUNK(ch, ws=" \t"):

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