From 5f35b0dbb9ebec63d805d230e01b4a0676e613af Mon Sep 17 00:00:00 2001
From: Tian Gao <gaogaotiantian@hotmail.com>
Date: Tue, 18 Jul 2023 15:37:36 -0700
Subject: [PATCH 1/2] Improve difflib performance with a cache

---
 Lib/difflib.py | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/Lib/difflib.py b/Lib/difflib.py
index ba0b256969ebff..a89393580bd132 100644
--- a/Lib/difflib.py
+++ b/Lib/difflib.py
@@ -371,20 +371,34 @@ def find_longest_match(self, alo=0, ahi=None, blo=0, bhi=None):
         # junk-free match ending with a[i-1] and b[j]
         j2len = {}
         nothing = []
+        b2jcache = {}
         for i in range(alo, ahi):
             # look at all instances of a[i] in b; note that because
             # b2j has no junk keys, the loop is skipped if a[i] is junk
             j2lenget = j2len.get
             newj2len = {}
-            for j in b2j.get(a[i], nothing):
-                # a[i] matches b[j]
-                if j < blo:
-                    continue
-                if j >= bhi:
-                    break
-                k = newj2len[j] = j2lenget(j-1, 0) + 1
-                if k > bestsize:
-                    besti, bestj, bestsize = i-k+1, j-k+1, k
+            if a[i] not in b2jcache:
+                cache = []
+                for j in b2j.get(a[i], nothing):
+                    # a[i] matches b[j]
+                    if j < blo:
+                        continue
+                    if j >= bhi:
+                        break
+                    cache.append(j)
+                    k = newj2len[j] = j2lenget(j-1, 0) + 1
+                    if k > bestsize:
+                        besti, bestj, bestsize = i-k+1, j-k+1, k
+                b2jcache[a[i]] = cache
+            else:
+                for j in b2jcache[a[i]]:
+                    # a[i] matches b[j]
+                    if j-1 in j2len:
+                        k = newj2len[j] = j2len[j-1] + 1
+                        if k > bestsize:
+                            besti, bestj, bestsize = i-k+1, j-k+1, k
+                    else:
+                        k = 1
             j2len = newj2len
 
         # Extend the best by non-junk elements on each end.  In particular,

From 0396f814eb56defa9adcc5433cc48ca08bd1f2c5 Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Tue, 18 Jul 2023 23:45:20 +0000
Subject: [PATCH 2/2] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../next/Library/2023-07-18-23-45-19.gh-issue-106865.dxO3Qr.rst  | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Library/2023-07-18-23-45-19.gh-issue-106865.dxO3Qr.rst

diff --git a/Misc/NEWS.d/next/Library/2023-07-18-23-45-19.gh-issue-106865.dxO3Qr.rst b/Misc/NEWS.d/next/Library/2023-07-18-23-45-19.gh-issue-106865.dxO3Qr.rst
new file mode 100644
index 00000000000000..3cece781a0a7af
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2023-07-18-23-45-19.gh-issue-106865.dxO3Qr.rst
@@ -0,0 +1 @@
+Improve performance of :func:`difflib.SequenceMatcher.find_longest_match` with a cache on hot path