LRU Cache with callback for eviction

We can use Python built-in functions.lru_cache, but when a cached item is evicted, there is no chance to release corresponding resources.

This LRU Cache with callback feature provides the similar usage as functions.lru_cache with decorator @lru_cache. Plus, it can task a eviction_callback function to do clean works. The function signature is callback(key, value).

Basic LRU Cache

@lru_cache(3)
def fetch(x):
    print('miss:', x, end='')
    return x + 1


for i in [1, 2, 3, 1, 2, 4, 3, 2, 1]:
    print(f'get data for {i}: ', end='')
    fetch(i)
    print()

Output:

get data for 1: miss: 1
get data for 2: miss: 2
get data for 3: miss: 3
get data for 1:
get data for 2:
get data for 4: miss: 4
get data for 3: miss: 3
get data for 2:
get data for 1: miss: 1

LRU Cache with callback for eviction

def eviction_callback(key, value):
    # release resources
    print(f"evicted key: {key}, {value}", end='')


@lru_cache(3, evict_callback=eviction_callback)
def fetch(x):
    print(f'miss: {x}, ', end='')
    return x + 1


for i in [1, 2, 3, 1, 2, 4, 3, 2, 1]:
    print(f'get data for {i}: ', end='')
    fetch(i)
    print()

Output:

get data for 1: miss: 1,
get data for 2: miss: 2,
get data for 3: miss: 3,
get data for 1:
get data for 2:
get data for 4: miss: 4, evicted key: 3, 4
get data for 3: miss: 3, evicted key: 1, 2
get data for 2:
get data for 1: miss: 1, evicted key: 4, 5