import weakref
class DoubleNode:
"""node for a double linked list """
previous = None
next = None
def __init__(self, value):
self.value = value
def extract(self):
previous = self.previous
next = self.next
if previous:
previous.next = next
if next:
next.previous = previous
self.next = self.previous = None
def insert_after(self, node):
self.next = node.next
self.previous = node
node.next.previous = self
node.next = self
class BufferCache:
"""Store data in a double linked list..."""
count = 0
def __init__(self, function, capacity=50):
self.cache = weakref.WeakValueDictionary()
self.next = self.previous = self
self.function = function
self.capacity = capacity
def _append(self, value):
""" append a node for a new value """
node = DoubleNode(value)
node.insert_after(self.previous)
if self.count == self.capacity:
self.next.extract()
else:
self.count += 1
return node
def _value(self, node):
"""return the value and put the node as the first one"""
node.extract()
node.insert_after(self.previous)
return node.value
def __call__(self, *args):
try:
node = self.cache[args]
except KeyError:
x = self.function(*args)
self.cache[args] = self._append(x)
else:
x = self._value(node)
return x
def __repr__(self):
i = self.previous
s = ""
while i!=self:
s = s + repr(i.value) + " "
i = i.previous
return s
#
# sample
#
def foo(x):
print "computing"
return "*" + str(x)
foo_cache = BufferCache(foo,5)
for i in range(5):
print foo_cache(i)
print foo_cache(2)
