shelved-cache

import cachetools from shelved_cache import PersistentCache from cachetools import LRUCache import os # Define a unique cache file path cache_file = "my_function_cache.db" # --- Cleanup any previous cache files for a clean run --- # shelve can create multiple files (.db, .bak, .dir, .dat) for ext in ["", ".bak", ".dir", ".dat"]: if os.path.exists(cache_file + ext): os.remove(cache_file + ext) # Initialize a persistent LRU cache, linking it to a file pc_for_square = PersistentCache(LRUCache, cache_file, maxsize=100) @cachetools.cached(pc_for_square) def square(x): print(f"Calculating square for {x}...") return x * x # First call: calculation happens result1 = square(5) print(f"First call: square(5) = {result1}") # Second call: result is retrieved from cache (no 'Calculating...' output) result2 = square(5) print(f"Second call: square(5) = {result2}") # A different argument will trigger a new calculation and cache entry result3 = square(10) print(f"Third call: square(10) = {result3}") # It's crucial to close the persistent cache to ensure data is written to disk. pc_for_square.close() print("\n--- Cache closed and reopened to demonstrate persistence ---") # Simulate a new application run or process by creating a new PersistentCache instance # linked to the *same* file. pc_reopened = PersistentCache(LRUCache, cache_file, maxsize=100) @cachetools.cached(pc_reopened) def square_reopened(x): # This should *not* print if the value was correctly persisted print(f"Calculating square (reopened) for {x}...") return x * x # This call should retrieve from the persisted cache without recalculating result_reopened = square_reopened(5) print(f"Reopened call: square_reopened(5) = {result_reopened}") pc_reopened.close() # --- Final cleanup of created cache files --- for ext in ["", ".bak", ".dir", ".dat"]: if os.path.exists(cache_file + ext): os.remove(cache_file + ext)