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# This file is part of MyPaint.
# Copyright (C) 2014-2018 by Andrew Chadwick <a.t.chadwick@gmail.com>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
from __future__ import division, print_function
from collections import OrderedDict
DEFAULT_CACHE_SIZE = 16384
class LRUCache (object):
"""Least-recently-used cache with dict-like usage"""
# The idea for using an OrderedDict comes from Kun Xi -
# http://www.kunxi.org/blog/2014/05/lru-cache-in-python/
_SENTINEL = object()
def __init__(self, capacity=DEFAULT_CACHE_SIZE):
self._capacity = capacity
self._cache = OrderedDict()
self._hits = 0
self._misses = 0
def __repr__(self):
hitrate = 1.0
missrate = 0.0
accesses = float(self._hits + self._misses)
if accesses > 0:
hitrate = self._hits / accesses
missrate = self._misses / accesses
return "<LRUCache c: %d/%d h: %.0f%% m: %.0f%%>" % (
len(self._cache),
self._capacity,
hitrate * 100,
missrate * 100,
)
def clear(self):
self._cache.clear()
self._hits = 0
self._misses = 0
def __len__(self):
return len(self._cache)
def __contains__(self, key):
return key in self._cache
def __getitem__(self, key):
item = self.get(key, self._SENTINEL)
if item is self._SENTINEL:
raise KeyError
return item
def get(self, key, default=None):
try:
item = self._cache.pop(key)
self._cache[key] = item
self._hits += 1
return item
except KeyError:
self._misses += 1
return default
def pop(self, key, default=_SENTINEL):
try:
item = self._cache.pop(key)
self._hits += 1
return item
except KeyError:
self._misses += 1
if default is LRUCache._SENTINEL:
raise
return default
def __setitem__(self, key, item):
try:
self._cache.pop(key)
except KeyError:
while len(self._cache) >= self._capacity:
self._cache.popitem(last=False)
self._cache[key] = item
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