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95 lines
3.0 KiB
Python
95 lines
3.0 KiB
Python
# -*- coding: utf-8 -*-
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#
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# Picard, the next-generation MusicBrainz tagger
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#
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# Copyright (C) 2017 Antonio Larrosa
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# Copyright (C) 2018-2021 Laurent Monin
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#
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# This program is free software; you can redistribute it and/or
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# modify it under the terms of the GNU General Public License
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# as published by the Free Software Foundation; either version 2
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# of the License, or (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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from collections.abc import MutableMapping
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class LRUCache(MutableMapping):
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"""
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Helper class to cache items using a Least Recently Used policy.
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It's originally used to cache generated pixmaps in the CoverArtBox object
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but it's generic enough to be used for other purposes if necessary.
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The cache will never hold more than max_size items and the item least
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recently used will be discarded.
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>>> cache = LRUCache(3)
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>>> cache['item1'] = 'some value'
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>>> cache['item2'] = 'some other value'
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>>> cache['item3'] = 'yet another value'
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>>> cache['item1']
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'some value'
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>>> cache['item4'] = 'This will push item 2 out of the cache'
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>>> cache['item2']
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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File "lrucache.py", line 48, in __getitem__
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return super().__getitem__(key)
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KeyError: 'item2'
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>>> cache['item5'] = 'This will push item3 out of the cache'
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>>> cache['item3']
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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File "lrucache.py", line 48, in __getitem__
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return super().__getitem__(key)
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KeyError: 'item3'
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>>> cache['item1']
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'some value'
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"""
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def __init__(self, max_size, *args, **kwargs):
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self._ordered_keys = []
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self._max_size = max_size
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self._dict = dict()
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for k, v in dict(*args, **kwargs).items():
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self[k] = v
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def __getitem__(self, key):
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value = self._dict[key]
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self._ordered_keys.remove(key)
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self._ordered_keys.insert(0, key)
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return value
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def __setitem__(self, key, value):
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if key in self:
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self._ordered_keys.remove(key)
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self._ordered_keys.insert(0, key)
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self._dict[key] = value
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if len(self) > self._max_size:
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item = self._ordered_keys.pop()
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del self._dict[item]
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def __delitem__(self, key):
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del self._dict[key]
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self._ordered_keys.remove(key)
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def __len__(self):
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return len(self._dict)
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def __iter__(self):
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return iter(self._dict)
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def __repr__(self):
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return repr(self._dict)
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