import anydbm
import cPickle as pickle
class pdict(object):
""" A persistent, lazy, caching, dictionary, using the anydbm module for
persistence. Keys must be basic strings (this is an anydbm limitation) and
values must be pickle-able objects. """
def __init__(self, file, mode):
""" Create new pdict using file. mode is passed to anydbm.open(). """
self._cache = {}
self._flush = {}
self._dbm = anydbm.open(file, mode)
def __contains__(self, key):
return key in self._cache or key in self._dbm
def __getitem__(self, key):
if key in self._cache:
return self._cache[key]
return self._cache.setdefault(key, pickle.loads(self._dbm[key]))
def __setitem__(self, key, value):
self._cache[key] = self._flush[key] = value
def __delitem__(self, key):
found = False
for data in (self._cache, self._flush, self._dbm):
if key in data:
del data[key]
found = True
if not found:
raise KeyError(key)
def keys(self):
keys = set(self._cache.keys())
keys.update(self._dbm.keys())
return keys
def sync(self):
for key, value in self._flush.iteritems():
self._dbm[key] = pickle.dumps(value, 2)
self._dbm.sync()
self._flush = {}
