Simplified caching of get_default_timezone().

django/test/signals.py

@@ -59,7 +59,7 @@ def update_connections_time_zone(**kwargs):
             time.tzset()
 
         # Reset local time zone cache
-        timezone._localtime = None
+        timezone.get_default_timezone.cache_clear()
 
     # Reset the database connections' time zone
     if kwargs['setting'] == 'USE_TZ' and settings.TIME_ZONE != 'UTC':

django/utils/timezone.py

@@ -15,6 +15,7 @@ except ImportError:
     pytz = None
 
 from django.conf import settings
+from django.utils import lru_cache
 from django.utils import six
 from django.utils.decorators import ContextDecorator
 
@@ -162,25 +163,21 @@ def get_fixed_timezone(offset):
     name = sign + hhmm
     return FixedOffset(offset, name)
 
-# In order to avoid accessing the settings at compile time,
-# wrap the expression in a function and cache the result.
-_localtime = None
-
 
+# In order to avoid accessing settings at compile time,
+# wrap the logic in a function and cache the result.
+@lru_cache.lru_cache()
 def get_default_timezone():
     """
     Returns the default time zone as a tzinfo instance.
 
     This is the time zone defined by settings.TIME_ZONE.
     """
-    global _localtime
-    if _localtime is None:
     if isinstance(settings.TIME_ZONE, six.string_types) and pytz is not None:
-            _localtime = pytz.timezone(settings.TIME_ZONE)
+        return pytz.timezone(settings.TIME_ZONE)
     else:
         # This relies on os.environ['TZ'] being set to settings.TIME_ZONE.
-            _localtime = LocalTimezone()
-    return _localtime
+        return LocalTimezone()
 
 
 # This function exists for consistency with get_current_timezone_name