lru.py 文件源码

def lfu_cache(maxsize=100):
    '''Least-frequenty-used cache decorator.

    Arguments to the cached function must be hashable.
    Cache performance statistics stored in f.hits and f.misses.
    Clear the cache with f.clear().
    http://en.wikipedia.org/wiki/Least_Frequently_Used

    '''
    def decorating_function(user_function):
        cache = {}                      # mapping of args to results
        use_count = Counter()           # times each key has been accessed
        kwd_mark = object()             # separate positional and keyword args

        @functools.wraps(user_function)
        def wrapper(*args, **kwds):
            key = args
            if kwds:
                key += (kwd_mark,) + tuple(sorted(kwds.items()))
            use_count[key] += 1

            # get cache entry or compute if not found
            try:
                result = cache[key]
                wrapper.hits += 1
            except KeyError:
                result = user_function(*args, **kwds)
                cache[key] = result
                wrapper.misses += 1

                # purge least frequently used cache entry
                if len(cache) > maxsize:
                    for key, _ in nsmallest(maxsize // 10,
                                            use_count.iteritems(),
                                            key=itemgetter(1)):
                        del cache[key], use_count[key]

            return result

        def clear():
            cache.clear()
            use_count.clear()
            wrapper.hits = wrapper.misses = 0

        wrapper.hits = wrapper.misses = 0
        wrapper.clear = clear
        return wrapper
    return decorating_function