Created
August 11, 2017 04:17
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A simple LRU cache implementation in Python. See test_lru.py for an usage example.
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class Item: | |
def __init__(self, key, value, previous, next): | |
self.key = key | |
self.value = value | |
self.previous = previous | |
self.next = next | |
class LRU: | |
def __init__(self, maxlength=10): | |
self.items = {} | |
self.head = None | |
self.tail = None | |
self.maxlength = maxlength | |
self.length = 0 | |
def get(self, key): | |
item = self.items.get(key) | |
if item is None: | |
return None | |
self.move_item_to_head(item) | |
return item.value | |
def put(self, key, value): | |
item = self.items.get(key) | |
if item is None: | |
self.prepend_item(key, value) | |
if self.length < self.maxlength: | |
self.length += 1 | |
else: | |
previous_tail = self.tail | |
del self.items[previous_tail.key] | |
tail = previous_tail.previous | |
tail.next = None | |
self.tail = tail | |
else: | |
item.value = value | |
self.move_item_to_head(item) | |
def move_item_to_head(self, item): | |
if self.head is item: | |
return | |
if self.tail is item: | |
self.tail = item.previous | |
self.tail.next = None | |
item.previous = None | |
item.next = self.head | |
self.head.previous = item | |
self.head = item | |
else: | |
item.previous.next = item.next | |
item.next.previous = item.previous | |
item.previous = None | |
item.next = self.head | |
self.head.previous = item | |
self.head = item | |
def prepend_item(self, key, value): | |
if self.head is None: | |
item = Item(key=key, value=value, previous=None, next=None) | |
self.head = item | |
self.tail = item | |
else: | |
item = Item(key=key, value=value, previous=None, next=self.head) | |
self.head.previous = item | |
self.head = item | |
self.items[key] = item | |
def __iter__(self): | |
now = self.head | |
while now is not None: | |
yield (now.key, now.value, ) | |
now = now.next | |
def __len__(self): | |
return self.length |
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from lru import LRU | |
def test_lru(): | |
yeah = LRU(maxlength=20) | |
for i in range(20): | |
yeah.put(i, i * i) | |
for i in range(20): | |
assert yeah.get(i) == i * i | |
assert len(yeah) == 20 | |
for i in range(20, 40): | |
yeah.put(i, i * i) | |
for i in range(20, 40): | |
assert yeah.get(i) == i * i | |
assert len(yeah) == 20 | |
for i in range(20): | |
assert yeah.get(i) is None | |
for i, (k, v) in enumerate(yeah): | |
assert k == 39 - i |
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