Show Lru.py syntax highlighted
# This file is derived from the GPL program "PyPE"
#
# Copyright (C) 2003-2006 Josiah Carlson
#
# 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
#
"""
Least recently used algorithm
"""
class Node:
"""
Node to be stored in the LRU structure
"""
def __init__(self, prev, value):
self.prev = prev
self.value = value
self.next = None
class LRU:
"""
Implementation of a length-limited O(1) LRU cache
"""
def __init__(self, count):
self.count = max(count, 2)
self.data = {}
self.first = None
self.last = None
def __contains__(self, obj):
"""
Returns True if the object is contained in the LRU
"""
return obj in self.data
def __getitem__(self, obj):
"""
Returns item assocated with Obj
"""
return self.data[obj].value[1]
def __setitem__(self, obj, val):
"""
Sets the item in the LRU, removing an old entry if needed
"""
if obj in self.data:
del self[obj]
nobj = Node(self.last, (obj, val))
if self.first is None:
self.first = nobj
if self.last:
self.last.next = nobj
self.last = nobj
self.data[obj] = nobj
if len(self.data) > self.count:
if self.first == self.last:
self.first = None
self.last = None
return
lnk = self.first
lnk.next.prev = None
self.first = lnk.next
lnk.next = None
del self.data[lnk.value[0]]
del lnk
def __delitem__(self, obj):
"""
Delete the object from the LRU
"""
nobj = self.data[obj]
if nobj.prev:
nobj.prev.next = nobj.next
else:
self.first = nobj.next
if nobj.next:
nobj.next.prev = nobj.prev
else:
self.last = nobj.prev
del self.data[obj]
def __iter__(self):
"""
Iterate over the LRU
"""
cur = self.first
while cur != None:
cur2 = cur.next
yield cur.value[1]
cur = cur2
raise StopIteration
def iteritems(self):
"""
Return items in the LRU using a generator
"""
cur = self.first
while cur != None:
cur2 = cur.next
yield cur.value
cur = cur2
raise StopIteration
def iterkeys(self):
"""
Return keys in the LRU using a generator
"""
return iter(self.data)
def itervalues(self):
"""
Return items and keys in the LRU using a generator
"""
for data in self.iteritems():
yield data[1]
def keys(self):
"""
Return all keys
"""
return [data[0] for data in self.iteritems()]
def values(self):
"""
Return all values
"""
return [data[1] for data in self.iteritems()]
def items(self):
"""
Return all items
"""
return [data[0] for data in self.iteritems()]
See more files for this project here