From: Sam Gross <colesbury@gmail.com>
Date: Tue, 10 Mar 2026 18:47:58 +0000 (-0400)
Subject: gh-142763: Fix race in ZoneInfo cache eviction (gh-144978)
X-Git-Tag: v3.15.0a8~366
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=665c1db94f46f8e1a18a8c2f89adb3bc72cb83dc;p=thirdparty%2FPython%2Fcpython.git

gh-142763: Fix race in ZoneInfo cache eviction (gh-144978)

The cache may be cleared between the evaluation of the if statement and the
call to popitem.
---

diff --git a/Lib/zoneinfo/_zoneinfo.py b/Lib/zoneinfo/_zoneinfo.py
index 3ffdb4c83719..bd3fefc6c9d9 100644
--- a/Lib/zoneinfo/_zoneinfo.py
+++ b/Lib/zoneinfo/_zoneinfo.py
@@ -47,7 +47,11 @@ class ZoneInfo(tzinfo):
         cls._strong_cache[key] = cls._strong_cache.pop(key, instance)
 
         if len(cls._strong_cache) > cls._strong_cache_size:
-            cls._strong_cache.popitem(last=False)
+            try:
+                cls._strong_cache.popitem(last=False)
+            except KeyError:
+                # another thread may have already emptied the cache
+                pass
 
         return instance
 
diff --git a/Misc/NEWS.d/next/Library/2025-12-18-00-00-00.gh-issue-142763.AJpZPVG5.rst b/Misc/NEWS.d/next/Library/2025-12-18-00-00-00.gh-issue-142763.AJpZPVG5.rst
new file mode 100644
index 000000000000..a5330365e3e4
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-12-18-00-00-00.gh-issue-142763.AJpZPVG5.rst
@@ -0,0 +1,2 @@
+Fix a race condition between :class:`zoneinfo.ZoneInfo` creation and
+:func:`zoneinfo.ZoneInfo.clear_cache` that could raise :exc:`KeyError`.