LRU cache

cache.py

'''Cache class for LRU'''

KEY_NOT_EXIST_VALUE = 'key-not-exist'


class LRUCache:
    '''
    Least recently used cache
    '''

    def __init__(self, size=10):
        self._store = {}
        self._size = size

    def put(self, key, value):
        '''Sets a key value in the cache'''
        if self._is_cache_full():
            self._delete_least_used()
        self.store[key] = value
        return True

    def get(self, key):
        '''Get a key value in the cache'''
        try:
            value = self.store.get(key, KEY_NOT_EXIST_VALUE)
            if value == KEY_NOT_EXIST_VALUE:
                return None
        except KeyError:
            return None

        self.store.pop(key, None)
        self.store[key] = value
        return value

    def _is_cache_full(self):
        return len(self.store.keys()) == self.size

    def _cache_key_exists(self, cache_key):
        for key in self.store:
            if cache_key == key:
                return True
        return False

    def _delete_least_used(self):
        least_used_key = list(self.store.keys())[0]
        self.store.pop(least_used_key)

    @property
    def size(self):
        '''Size property getter'''
        return self._size

    @property
    def store(self):
        'Store property getter'
        return self._store

main.py

'''Runs the cache implemetation '''
from cache.cache import LRUCache


def main():
    '''Tests the cache logic'''
    print('Cache of size 3 is created')
    cache = LRUCache(3)
    print('Put a=>1, b=>2, c=>3 and d=>4')
    cache.put('a', 1)
    cache.put('b', 2)
    cache.put('c', 3)
    cache.put('d', 4)

    # Query non-existing
    print('Query non-existing a')
    print(cache.get('a'), end="\n\n")

    # Query existing
    print('Query existing b and c')
    print(cache.get('b'))
    print(cache.get('c'), end="\n\n")

    # Put new value
    print('Put new value e => 5')
    cache.put('e', 5)

    # Least used cache which is 'd' should be removed
    # None is returned
    print('Query d and should get None because it was LRU cache and removed')
    print(cache.get('d'))


main()