lru_cache.py

from collections import OrderedDict


class LRUCache:

    # initialising capacity
    def __init__(self, capacity: int):
        self.cache = OrderedDict()
        self.capacity = capacity

    # we return the value of the key
    # that is queried in O(1) and return -1 if we
    # don't find the key in out dict / cache.
    # And also move the key to the end
    # to show that it was recently used.
    def get(self, key: int) -> int:
        if key not in self.cache:
            return -1
        else:
            self.cache.move_to_end(key)
            return self.cache[key]

    # first, we add / update the key by conventional methods.
    # And also move the key to the end to show that it was recently used.
    # But here we will also check whether the length of our
    # ordered dictionary has exceeded our capacity,
    # If so we remove the first key (least recently used)
    def put(self, key: int, value) -> None:
        self.cache[key] = value
        self.cache.move_to_end(key)
        if len(self.cache) > self.capacity:
            self.cache.popitem(last=False)


# RUNNER
# Press the green button in the gutter to run the script.
if __name__ == '__main__':
    # initializing our cache with the capacity of 2
    cache = LRUCache(2)
    cache.put(3, {"march1": 123})
    print(cache.cache)
    cache.put(1, 1)
    print(cache.cache)
    cache.put(2, 2)
    print(cache.cache)
    cache.get(1)
    print(cache.cache)
    cache.get(2)
    print(cache.cache)
    cache.put(4, 4)
    print(cache.cache)
    cache.get(1)
    print(cache.cache)
    cache.get(3)
    print(cache.cache)
    cache.get(4)
    print(cache.cache)