Python/other/least_recently_used.py
Andrew Grangaard 551c65766d
[Mypy] fix other/least_recently_used ()
* makes LRUCache constructor concrete

* fixes bug in dq_removal in other/least_recently_used

+ deque.remove() operates by value not index

* [mypy] Annotates other/least_recently_used over generic type

+ clean-up: rename key_reference to match type.

* [mypy] updates example to demonstrate LRUCache with complex type

* Adds doctest to other/least_recently_used

* mypy.ini: Remove exclude = (other/least_recently_used.py)

* Various mypy configs

* Delete mypy.ini

* Add mypy to .pre-commit-config.yaml

* mypy --ignore-missing-imports --install-types --non-interactive .

* mypy v0.910

* Pillow=8.3.7

* Pillow==8.3.7

* Pillow==8.3.2

* Update .pre-commit-config.yaml

* Update requirements.txt

* Update pre-commit.yml

* --install-types  # See mirrors-mypy README.md

Co-authored-by: Christian Clauss <cclauss@me.com>
2021-11-16 15:01:17 +01:00

93 lines
2.4 KiB
Python

from __future__ import annotations
import sys
from collections import deque
from typing import Generic, TypeVar
T = TypeVar("T")
class LRUCache(Generic[T]):
"""
Page Replacement Algorithm, Least Recently Used (LRU) Caching.
>>> lru_cache: LRUCache[str | int] = LRUCache(4)
>>> lru_cache.refer("A")
>>> lru_cache.refer(2)
>>> lru_cache.refer(3)
>>> lru_cache
LRUCache(4) => [3, 2, 'A']
>>> lru_cache.refer("A")
>>> lru_cache
LRUCache(4) => ['A', 3, 2]
>>> lru_cache.refer(4)
>>> lru_cache.refer(5)
>>> lru_cache
LRUCache(4) => [5, 4, 'A', 3]
"""
dq_store: deque[T] # Cache store of keys
key_reference: set[T] # References of the keys in cache
_MAX_CAPACITY: int = 10 # Maximum capacity of cache
def __init__(self, n: int) -> None:
"""Creates an empty store and map for the keys.
The LRUCache is set the size n.
"""
self.dq_store = deque()
self.key_reference = 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: T) -> None:
"""
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:
if len(self.dq_store) == LRUCache._MAX_CAPACITY:
last_element = self.dq_store.pop()
self.key_reference.remove(last_element)
else:
self.dq_store.remove(x)
self.dq_store.appendleft(x)
self.key_reference.add(x)
def display(self) -> None:
"""
Prints all the elements in the store.
"""
for k in self.dq_store:
print(k)
def __repr__(self) -> str:
return f"LRUCache({self._MAX_CAPACITY}) => {list(self.dq_store)}"
if __name__ == "__main__":
import doctest
doctest.testmod()
lru_cache: LRUCache[str | int] = LRUCache(4)
lru_cache.refer("A")
lru_cache.refer(2)
lru_cache.refer(3)
lru_cache.refer("A")
lru_cache.refer(4)
lru_cache.refer(5)
lru_cache.display()
print(lru_cache)
assert str(lru_cache) == "LRUCache(4) => [5, 4, 'A', 3]"