60 lines
1.9 KiB
Python
60 lines
1.9 KiB
Python
# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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import collections
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import logging
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import shelve
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LOG = logging.getLogger(__name__)
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class Cache:
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"""Data cache with transparent key management
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Keys passed to methods are expected to be tuples of strings but
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are converted to something the underlying implementation can
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store and retrieve.
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Values stored in the cache are pickled before being written and
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unpickled before being returned.
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"""
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def __init__(self, filename, preload=True):
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self._shelf = shelve.open(filename)
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self._memory = {}
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if preload:
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LOG.debug('loading cache into RAM')
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for key in self._shelf:
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self._memory[key] = self._shelf[key]
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LOG.debug('loaded %d items from cache', len(self._memory))
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self._data = collections.ChainMap(self._memory, self._shelf)
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def __contains__(self, key):
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return self._mk_key(key) in self._data
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def _mk_key(self, key):
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return ':'.join(str(k) for k in key)
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def __setitem__(self, key, value):
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self._shelf[self._mk_key(key)] = value
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def __getitem__(self, key):
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return self._data[self._mk_key(key)]
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def __delitem__(self, key):
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real_key = self._mk_key(key)
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if real_key in self._shelf:
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del self._shelf[real_key]
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if real_key in self._memory:
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del self._memory[real_key]
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