| import collections |
| |
| from .cache import Cache |
| |
| |
| class LFUCache(Cache): |
| """Least Frequently Used (LFU) cache implementation.""" |
| |
| def __init__(self, maxsize, missing=None, getsizeof=None): |
| Cache.__init__(self, maxsize, missing, getsizeof) |
| self.__counter = collections.Counter() |
| |
| def __getitem__(self, key, cache_getitem=Cache.__getitem__): |
| value = cache_getitem(self, key) |
| self.__counter[key] -= 1 |
| return value |
| |
| def __setitem__(self, key, value, cache_setitem=Cache.__setitem__): |
| cache_setitem(self, key, value) |
| self.__counter[key] -= 1 |
| |
| def __delitem__(self, key, cache_delitem=Cache.__delitem__): |
| cache_delitem(self, key) |
| del self.__counter[key] |
| |
| def popitem(self): |
| """Remove and return the `(key, value)` pair least frequently used.""" |
| try: |
| (key, _), = self.__counter.most_common(1) |
| except ValueError: |
| raise KeyError('%s is empty' % self.__class__.__name__) |
| else: |
| return (key, self.pop(key)) |
