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