From d37fb559102d9c20786d8578a0362d1cd44aada2 Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <python@rcn.com>
Date: Fri, 16 Mar 2012 17:04:11 -0700
Subject: Unique sentinel value for cache.get()

---
 Lib/functools.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Lib/functools.py b/Lib/functools.py
index adc7927..3eb55c6 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -175,8 +175,8 @@ def lru_cache(maxsize=100, typed=False):
                 # simple caching without ordering or size limit
                 nonlocal hits, misses
                 key = make_key(args, kwds, typed) if kwds or typed else args
-                result = cache_get(key)
-                if result is not None:
+                result = cache_get(key, root)   # root used here as a unique not-found sentinel        
+                if result is not root:
                     hits += 1
                     return result
                 result = user_function(*args, **kwds)
-- 
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