Fix-up comments and add a sentinel variable for clarity.
diff --git a/Lib/functools.py b/Lib/functools.py
index 5cf8f1c..6df75ed 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -154,8 +154,8 @@
Arguments to the cached function must be hashable.
- View the cache statistics named tuple (hits, misses, maxsize, currsize) with
- f.cache_info(). Clear the cache and statistics with f.cache_clear().
+ View the cache statistics named tuple (hits, misses, maxsize, currsize)
+ with f.cache_info(). Clear the cache and statistics with f.cache_clear().
Access the underlying function with f.__wrapped__.
See: http://en.wikipedia.org/wiki/Cache_algorithms#Least_Recently_Used
@@ -169,18 +169,19 @@
def decorating_function(user_function):
- cache = dict()
+ cache = {}
hits = misses = 0
- kwd_mark = (object(),) # separate positional and keyword args
- cache_get = cache.get # bound method to lookup key or return None
- _len = len # localize the global len() function
- lock = Lock() # because linkedlist updates aren't threadsafe
- root = [] # root of the circular doubly linked list
- root[:] = [root, root, None, None] # initialize by pointing to self
- PREV, NEXT, KEY, RESULT = 0, 1, 2, 3 # names for the link fields
+ kwd_mark = (object(),) # separate positional and keyword args
+ cache_get = cache.get # bound method to lookup key or return None
+ sentinel = object() # unique object used with cache_get
+ _len = len # localize the global len() function
+ lock = Lock() # because linkedlist updates aren't threadsafe
+ root = [] # root of the circular doubly linked list
+ root[:] = [root, root, None, None] # initialize by pointing to self
+ PREV, NEXT, KEY, RESULT = 0, 1, 2, 3 # names for the link fields
def make_key(args, kwds, typed, tuple=tuple, sorted=sorted, type=type):
- # helper function to build a cache key from positional and keyword args
+ # build a cache key from positional and keyword args
key = args
if kwds:
sorted_items = tuple(sorted(kwds.items()))
@@ -194,7 +195,7 @@
if maxsize == 0:
def wrapper(*args, **kwds):
- # no caching, just do a statistics update after a successful call
+ # no caching, just a statistics update after a successful call
nonlocal misses
result = user_function(*args, **kwds)
misses += 1
@@ -206,8 +207,8 @@
# 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, root) # root used here as a unique not-found sentinel
- if result is not root:
+ result = cache_get(key, sentinel)
+ if result is not sentinel:
hits += 1
return result
result = user_function(*args, **kwds)
@@ -224,7 +225,7 @@
with lock:
link = cache_get(key)
if link is not None:
- # record recent use of the key by moving it to the front of the list
+ # move the link to the front of the circular queue
link_prev, link_next, key, result = link
link_prev[NEXT] = link_next
link_next[PREV] = link_prev
@@ -237,7 +238,7 @@
result = user_function(*args, **kwds)
with lock:
if _len(cache) < maxsize:
- # put result in a new link at the front of the list
+ # put result in a new link at the front of the queue
last = root[PREV]
link = [last, root, key, result]
cache[key] = last[NEXT] = root[PREV] = link