87 строки
3.0 KiB
Python
87 строки
3.0 KiB
Python
# http://code.activestate.com/recipes/498245-lru-and-lfu-cache-decorators/
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# by Raymond Hettinger.
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import collections
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import functools
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from itertools import ifilterfalse
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class Counter(dict):
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'Mapping where default values are zero'
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def __missing__(self, key):
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return 0
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def lru_cache(maxsize=100):
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'''Least-recently-used cache decorator.
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Arguments to the cached function must be hashable.
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Cache performance statistics stored in f.hits and f.misses.
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Clear the cache with f.clear().
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http://en.wikipedia.org/wiki/Cache_algorithms#Least_Recently_Used
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'''
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maxqueue = maxsize * 10
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def decorating_function(user_function,
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len=len, iter=iter, tuple=tuple, sorted=sorted, KeyError=KeyError):
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cache = {} # mapping of args to results
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queue = collections.deque() # order that keys have been used
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refcount = Counter() # times each key is in the queue
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sentinel = object() # marker for looping around the queue
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kwd_mark = object() # separate positional and keyword args
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# lookup optimizations (ugly but fast)
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queue_append, queue_popleft = queue.append, queue.popleft
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queue_appendleft, queue_pop = queue.appendleft, queue.pop
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@functools.wraps(user_function)
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def wrapper(*args, **kwds):
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# cache key records both positional and keyword args
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key = args
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if kwds:
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key += (kwd_mark,) + tuple(sorted(kwds.items()))
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# record recent use of this key
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queue_append(key)
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refcount[key] += 1
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# get cache entry or compute if not found
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try:
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result = cache[key]
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wrapper.hits += 1
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except KeyError:
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result = user_function(*args, **kwds)
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cache[key] = result
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wrapper.misses += 1
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# purge least recently used cache entry
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if len(cache) > maxsize:
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key = queue_popleft()
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refcount[key] -= 1
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while refcount[key]:
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key = queue_popleft()
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refcount[key] -= 1
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del cache[key], refcount[key]
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# periodically compact the queue by eliminating duplicate keys
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# while preserving order of most recent access
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if len(queue) > maxqueue:
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refcount.clear()
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queue_appendleft(sentinel)
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for key in ifilterfalse(refcount.__contains__,
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iter(queue_pop, sentinel)):
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queue_appendleft(key)
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refcount[key] = 1
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return result
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def clear():
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cache.clear()
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queue.clear()
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refcount.clear()
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wrapper.hits = wrapper.misses = 0
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wrapper.hits = wrapper.misses = 0
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wrapper.clear = clear
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return wrapper
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return decorating_function
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