Congratulations, you made it! We've been on a journey to expand our simple key-value store and have added integral features such as expiration times and LRU caching, learning from the popular data store, Redis.

Our key-value store has been revved up. It can now hold values for a specified time and uses LRU caching for handling keys when memory capacity becomes a potential concern while also preserving performance. We mimic Redis in two main aspects: fast access to stored data and optimized memory use.

The expanded key-value store can now be seen as a rudimentary version of Redis, the ultra-fast, in-memory data store with rich data structure support. Does it mean our key-value store is as powerful as Redis? Not entirely, because Redis has much more complex features (such as data replication, persistence options, various types of data structures, built-in Lua scripting, etc.). However, we've gained a glimpse into the inner workings of Redis and built something similar. This can be a great confidence booster, ever boosting your understanding of computer science and software development.

Here's the final snapshot of our key-value store implemented in Python:

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if __name__ == '__main__':

    from collections import OrderedDict

    import time

​

    class LRU_Cache:

        def __init__(self, capacity):

            self.capacity = capacity

            self.cache = OrderedDict()

​

        def get(self, key):

            try:

                value = self.cache.pop(key)

                self.cache[key] = value

                return value

            except KeyError:

                return -1

​

        def put(self, key, value):

            try:

                self.cache.pop(key)

            except KeyError:

                if len(self.cache) >= self.capacity:

                    self.cache.popitem(last=False)

            self.cache[key] = value

​

    key_value_store = LRU_Cache(3)

    key_value_store.put(1, 'value1')

    key_value_store.put(2, 'value2')

    print(key_value_store.get(1))  # Output: 'value1'