"""
An in-memory cache that expires keys after a given time.

# Example usage
cache = KeyValueCache()
cache.set('key1', 'value1')
cache.set('key2', 'value2')

print(cache.get('key1'))  # Output: value1
print(cache.get('key2'))  # Output: value2

time.sleep(5)

print(cache.get('key1'))  # Output: None (expired)
print(cache.get('key2'))  # Output: None (expired)

"""

import threading
import time


class KeyValueCache:
    def __init__(self):
        self._cache = {}
        self._lock = threading.Lock()

    def set(self, key, value, expiration=5):
        with self._lock:
            self._cache[key] = {
                "value": value,
                "expiration_time": time.time() + expiration,
            }

    def get(self, key):
        with self._lock:
            if key in self._cache:
                item = self._cache[key]
                if item["expiration_time"] > time.time():
                    return item["value"]
                else:
                    del self._cache[key]
        return None