Speed optimization ("is" is much faster than "isinstance").

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@29696 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Type/CachePlugins/RamCache.py

@@ -73,8 +73,8 @@ class RamCache(BaseCache):
 
   def get(self, cache_id, scope, default=_MARKER):
     cache = self.getCacheStorage()
-    cache_entry = cache.get((scope, cache_id), default)
-    if isinstance(cache_entry, CacheEntry):
+    cache_entry = cache.get((scope, cache_id), _MARKER)
+    if cache_entry is not _MARKER:
       if not cache_entry.isExpired():
         #The value is well retrieved from cache storage
         cache_entry.markCacheHit()