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Refactor calculation of the cache key. Minor code cleanups.

This commit is contained in:
Raymond Hettinger 2012-03-16 16:53:05 -07:00
parent e80b29b5b6
commit 6e8c817687
1 changed files with 21 additions and 25 deletions
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46
Lib/functools.py
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@ -146,31 +146,35 @@ def lru_cache(maxsize=100, typed=False):
# The internals of the lru_cache are encapsulated for thread safety and
# to allow the implementation to change (including a possible C version).
def decorating_function(user_function,
*, tuple=tuple, sorted=sorted, map=map, len=len, type=type):
def decorating_function(user_function):
cache = dict()
hits = misses = 0
cache_get = cache.get # bound method for fast lookup
kwd_mark = (object(),) # separates positional and keyword args
lock = Lock() # needed because linkedlist isn't threadsafe
root = [] # root of circular doubly linked list
cache_get = cache.get # bound method to lookup key or return None
_len = len # localize the global len() function
kwd_mark = (object(),) # separate positional and keyword args
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 of link fields
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):
key = args
if kwds:
sorted_items = tuple(sorted(kwds.items()))
key += kwd_mark + sorted_items
if typed:
key += tuple(type(v) for v in args)
if kwds:
key += tuple(type(v) for k, v in sorted_items)
return key
if maxsize is None:
@wraps(user_function)
def wrapper(*args, **kwds):
# simple caching without ordering or size limit
nonlocal hits, misses
key = args
if kwds:
sorted_items = tuple(sorted(kwds.items()))
key += kwd_mark + sorted_items
if typed:
key += tuple(map(type, args))
if kwds:
key += tuple(type(v) for k, v in sorted_items)
key = make_key(args, kwds, typed) if kwds or typed else args
result = cache_get(key)
if result is not None:
hits += 1
@ -184,14 +188,7 @@ def lru_cache(maxsize=100, typed=False):
def wrapper(*args, **kwds):
# size limited caching that tracks accesses by recency
nonlocal hits, misses
key = args
if kwds:
sorted_items = tuple(sorted(kwds.items()))
key += kwd_mark + sorted_items
if typed:
key += tuple(map(type, args))
if kwds:
key += tuple(type(v) for k, v in sorted_items)
key = make_key(args, kwds, typed) if kwds or typed else args
with lock:
link = cache_get(key)
if link is not None:
@ -210,7 +207,7 @@ def lru_cache(maxsize=100, typed=False):
last = root[PREV]
link = [last, root, key, result]
cache[key] = last[NEXT] = root[PREV] = link
if len(cache) > maxsize:
if _len(cache) > maxsize:
# purge least recently used cache entry
old_prev, old_next, old_key, old_result = root[NEXT]
root[NEXT] = old_next
@ -229,7 +226,6 @@ def lru_cache(maxsize=100, typed=False):
nonlocal hits, misses, root
with lock:
cache.clear()
root = []
root[:] = [root, root, None, None]
hits = misses = 0