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import collections
from .cache import Cache
class LRUCache(Cache):
"""Least Recently Used (LRU) cache implementation."""
def __init__(self, maxsize, getsizeof=None):
Cache.__init__(self, maxsize, getsizeof)
self.__order = collections.OrderedDict()
def __getitem__(self, key, cache_getitem=Cache.__getitem__):
value = cache_getitem(self, key)
if key in self: # __missing__ may not store item
self.__update(key)
return value
def __setitem__(self, key, value, cache_setitem=Cache.__setitem__):
cache_setitem(self, key, value)
self.__update(key)
def __delitem__(self, key, cache_delitem=Cache.__delitem__):
cache_delitem(self, key)
del self.__order[key]
def popitem(self):
"""Remove and return the `(key, value)` pair least recently used."""
try:
key = next(iter(self.__order))
except StopIteration:
raise KeyError("%s is empty" % type(self).__name__) from None
else:
return (key, self.pop(key))
def __update(self, key):
try:
self.__order.move_to_end(key)
except KeyError:
self.__order[key] = None
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