Package translate :: Package misc :: Module lru
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Source Code for Module translate.misc.lru

  1  #!/usr/bin/env python 
  2  # -*- coding: utf-8 -*- 
  3  # 
  4  # Copyright 2009 Zuza Software Foundation 
  5  # 
  6  # This file is part of translate. 
  7  # 
  8  # This program is free software; you can redistribute it and/or modify 
  9  # it under the terms of the GNU General Public License as published by 
 10  # the Free Software Foundation; either version 2 of the License, or 
 11  # (at your option) any later version. 
 12  # 
 13  # This program is distributed in the hope that it will be useful, 
 14  # but WITHOUT ANY WARRANTY; without even the implied warranty of 
 15  # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
 16  # GNU General Public License for more details. 
 17  # 
 18  # You should have received a copy of the GNU General Public License 
 19  # along with this program; if not, see <http://www.gnu.org/licenses/>. 
 20   
 21  from collections import deque 
 22  from weakref import WeakValueDictionary 
 23  import gc 
 24   
25 -class LRUCachingDict(WeakValueDictionary):
26 """Caching dictionary like object that discards the least recently 27 used objects when number of cached items exceeds maxsize. 28 29 cullsize is the fraction of items that will be discarded when 30 maxsize is reached. 31 """ 32
33 - def __init__(self, maxsize, cullsize=2, *args, **kwargs):
34 self.cullsize = max(2, cullsize) 35 self.maxsize = max(cullsize, maxsize) 36 self.queue = deque() 37 WeakValueDictionary.__init__(self, *args, **kwargs)
38
39 - def __setitem__(self, key, value):
40 # check boundaries to minimiza duplicate references 41 while len(self.queue) and self.queue[0][0] == key: 42 # item at left end of queue pop it since it'll be appended 43 # to right 44 self.queue.popleft() 45 46 while len(self.queue) and self.queue[-1][0] == key: 47 # item at right end of queue pop it since it'll be 48 # appended again 49 self.queue.pop() 50 51 if len(self) >= self.maxsize: 52 # maximum cache size exceeded, cull old items 53 # 54 # note queue is the real cache but its size is boundless 55 # since it might have duplicate references. 56 # 57 # don't bother culling if queue is smaller than weakref, 58 # this means there are too many references outside the 59 # cache, culling won't free much memory (if any). 60 while len(self) >= self.maxsize <= len(self.queue): 61 cullsize = max(int(len(self.queue) / self.cullsize), 2) 62 try: 63 for i in range(cullsize): 64 self.queue.popleft() 65 except IndexError: 66 # queue is empty, bail out. 67 break 68 finally: 69 # call garbage collecter manually since objects 70 # with circular references take some time to get 71 # collected 72 for i in range(5): 73 if gc.collect() == 0: 74 break 75 self.queue.append((key, value)) 76 WeakValueDictionary.__setitem__(self, key, value)
77 78
79 - def __getitem__(self, key):
80 value = WeakValueDictionary.__getitem__(self, key) 81 # check boundaries to minimiza duplicate references 82 while len(self.queue) > 0 and self.queue[0][0] == key: 83 # item at left end of queue pop it since it'll be appended 84 # to right 85 self.queue.popleft() 86 87 # only append if item is not at right end of queue 88 if not (len(self.queue) and self.queue[-1][0] == key): 89 self.queue.append((key, value)) 90 91 return value
92
93 - def __delitem__(self, key):
94 # can't efficiently find item in queue to delete, check 95 # boundaries. otherwise just wait till next cache purge 96 while len(self.queue) and self.queue[0][0] == key: 97 # item at left end of queue pop it since it'll be appended 98 # to right 99 self.queue.popleft() 100 101 while len(self.queue) and self.queue[-1][0] == key: 102 # item at right end of queue pop it since it'll be 103 # appended again 104 self.queue.pop() 105 106 return WeakValueDictionary.__delitem__(self, key)
107
108 - def clear(self):
109 self.queue.clear() 110 return WeakValueDictionary.clear(self)
111
112 - def setdefault(self, key, default):
113 if key not in self: 114 self[key]=default 115 116 return self[key]
117