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import collections
from .cache import Cache
class LFUCache(Cache):
"""Least Frequently Used (LFU) cache implementation."""
def __init__(self, maxsize, getsizeof=None):
Cache.__init__(self, maxsize, getsizeof)
self.__counter = collections.Counter()
def __getitem__(self, key, cache_getitem=Cache.__getitem__):
value = cache_getitem(self, key)
if key in self: # __missing__ may not store item
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" % type(self).__name__) from None
else:
return (key, self.pop(key))
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