gh-142763: Fix race in ZoneInfo cache eviction

colesbury · colesbury · commit 6c4f783e77b0 · 2026-02-18T17:13:54.000-05:00
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 +1,3 @@
+Fix a race condition in :class:`zoneinfo.ZoneInfo` cache eviction that could
+raise :exc:`KeyError` when multiple threads create :class:`~zoneinfo.ZoneInfo`
+instances concurrently.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+Fix a race condition in :class:`zoneinfo.ZoneInfo` cache eviction that could
	`2`	+raise :exc:`KeyError` when multiple threads create :class:`~zoneinfo.ZoneInfo`
	`3`	`+instances concurrently.`