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# 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.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# this program; if not, write to the Free Software Foundation, Inc.,
# 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
""" Copyright (c) 2002-2003 LOGILAB S.A. (Paris, FRANCE).
http://www.logilab.fr/ -- mailto:contact@logilab.fr
Cache module, with a least recently used algorithm for the management of the
deletion of entries.
"""
_marker = object()
class Cache:
""" a dictionnary like cache
inv:
len(self._usage) <= self.size
len(self.data) <= self.size
"""
def __init__(self, size=100):
self.data = {}
self.size = size
self._usage = []
def __repr__(self):
return repr(self.data)
def __len__(self):
return len(self.data)
def _update_usage(self, key):
# Special case : cache's size = 0 !
if self.size <= 0:
return
if not self._usage:
self._usage.append(key)
elif self._usage[-1] != key:
try:
self._usage.remove(key)
except ValueError:
# we are inserting a new key
# check the size of the dictionnary
# and remove the oldest item in the cache
if self.size and len(self._usage) >= self.size:
del self.data[self._usage[0]]
del self._usage[0]
self._usage.append(key)
else:
pass # key is already the most recently used key
def __getitem__(self, key):
value = self.data[key]
self._update_usage(key)
return value
def __setitem__(self, key, item):
# Just make sure that size > 0 before inserting a new item in the cache
if self.size > 0:
self.data[key] = item
self._update_usage(key)
def __delitem__(self, key):
# If size <= 0, then we don't have anything to do
# XXX FIXME : Should we let the 'del' raise a KeyError ?
if self.size > 0:
del self.data[key]
self._usage.remove(key)
def pop(self, value, default=_marker):
if value in self.data:
self._usage.remove(value)
if default is _marker:
return self.data.pop(value)
return self.data.pop(value, default)
def clear(self):
self.data.clear()
self._usage = []
def keys(self):
return self.data.keys()
def items(self):
return self.data.items()
def values(self):
return self.data.values()
def has_key(self, key):
return self.data.has_key(key)
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