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

colesbury · ljfp · commit f44e4d11bcf6 · 2026-04-25T17:51:38.000+02:00
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
@@ -47,7 +47,11 @@ def __new__(cls, key):
         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
@@ -0,0 +1,2 @@
+Fix a race condition between :class:`zoneinfo.ZoneInfo` creation and
+:func:`zoneinfo.ZoneInfo.clear_cache` that could raise :exc:`KeyError`.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Fix a race condition between :class:`zoneinfo.ZoneInfo` creation and
	`2`	+:func:`zoneinfo.ZoneInfo.clear_cache` that could raise :exc:`KeyError`.