How to Implement a Negative Cache with TTL in Python

from time import time, sleep

class TTLMockCache:
    def __init__(self, ttl_seconds=5):
        self.ttl = ttl_seconds
        self.store = {}
        self.negative_cache = {}

    def get(self, key):
        now = time()
        if key in self.store:
            value, expires_at = self.store[key]
            if expires_at > now:
                return value
            else:
                del self.store[key]
        if key in self.negative_cache:
            neg_expires_at = self.negative_cache[key]
            if neg_expires_at > now:
                return None  # negative cache hit
            else:
                del self.negative_cache[key]
        # Not found: populate negative cache
        self.negative_cache[key] = now + self.ttl
        return None

    def put(self, key, value, ttl=60):
        self.store[key] = (value, time() + ttl)
        self.negative_cache.pop(key, None)


if __name__ == "__main__":
    cache = TTLMockCache(ttl_seconds=2)
    print(cache.get("missing"))          # None → negative cached
    sleep(1)
    print(cache.get("missing"))          # None (negative hit)
    cache.put("missing", "real-value")   # overrides negative
    print(cache.get("missing"))          # "real-value"
    sleep(3)                             # TTL expired, negative cleared
    print(cache.get("expired-neg"))      # None again, re-negative