from time import monotonic class LRUCache: """ LRUCache is a least-recently-used (LRU) cache with expiry time. Attributes: open (callable): Function to open a new handle. capacity (int): Max number of items in the cache. maxage (float): Max age for items in cache in seconds. cache (list): Internal list storing the cache items. """ def __init__(self, open: callable, *, capacity: int, maxage: float): """ Initialize LRUCache. Args: open (callable): Function to open a new handle. capacity (int): Maximum capacity of the cache. maxage (float): Max age for items in cache in seconds. """ self.open = open self.capacity = capacity self.maxage = maxage self.cache = [] # Each item is a tuple: (key, handle, timestamp), recent items first def __contains__(self, key): """Check if key is in cache.""" return any(rec[0] == key for rec in self.cache) def __getitem__(self, key): """ Retrieve an item by its key. Args: key: The key to retrieve. Returns: The corresponding item's handle. """ # Take from cache or open a new one for i, (k, f, ts) in enumerate(self.cache): if k == key: self.cache.pop(i) break else: f = self.open(key) # Add/restore to end of cache self.cache.insert(0, (key, f, monotonic())) self.expire_items() print(self.cache) return f def expire_items(self): """ Expire items that are either too old or exceed cache capacity. """ ts = monotonic() - self.maxage while len(self.cache) > self.capacity or self.cache and self.cache[-1][2] < ts: self.cache.pop()[1].close() def close(self): """ Close the cache and remove all items. """ self.capacity = 0 self.expire_items()