Python/other/least_recently_used.py

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import sys
from abc import abstractmethod
from collections import deque
class LRUCache:
""" Page Replacement Algorithm, Least Recently Used (LRU) Caching."""
dq_store = object() # Cache store of keys
key_reference_map = object() # References of the keys in cache
_MAX_CAPACITY: int = 10 # Maximum capacity of cache
@abstractmethod
def __init__(self, n: int):
""" Creates an empty store and map for the keys.
The LRUCache is set the size n.
"""
self.dq_store = deque()
self.key_reference_map = set()
if not n:
LRUCache._MAX_CAPACITY = sys.maxsize
elif n < 0:
raise ValueError("n should be an integer greater than 0.")
else:
LRUCache._MAX_CAPACITY = n
def refer(self, x):
"""
Looks for a page in the cache store and adds reference to the set.
Remove the least recently used key if the store is full.
Update store to reflect recent access.
"""
if x not in self.key_reference_map:
if len(self.dq_store) == LRUCache._MAX_CAPACITY:
last_element = self.dq_store.pop()
self.key_reference_map.remove(last_element)
else:
index_remove = 0
for idx, key in enumerate(self.dq_store):
if key == x:
index_remove = idx
break
self.dq_store.remove(index_remove)
self.dq_store.appendleft(x)
self.key_reference_map.add(x)
def display(self):
"""
Prints all the elements in the store.
"""
for k in self.dq_store:
print(k)
if __name__ == "__main__":
lru_cache = LRUCache(4)
lru_cache.refer(1)
lru_cache.refer(2)
lru_cache.refer(3)
lru_cache.refer(1)
lru_cache.refer(4)
lru_cache.refer(5)
lru_cache.display()