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.

Author: colesbury

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
 

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`.