Store the cache to a file functools.lru_cache in Python >= 3.2

Consider using joblib.Memory for persistent caching to the disk.

Since the disk is enormous, there's no need for an LRU caching scheme.

You can't do what you want using lru_cache, since it doesn't provide an API to access the cache, and it might be rewritten in C in future releases. If you really want to save the cache you have to use a different solution that gives you access to the cache.

It's simple enough to write a cache yourself. For example:

from functools import wraps

def cached(func):
    func.cache = {}
    @wraps(func)
    def wrapper(*args):
        try:
            return func.cache[args]
        except KeyError:
            func.cache[args] = result = func(*args)
            return result   
    return wrapper

You can then apply it as a decorator:

>>> @cached
... def fibonacci(n):
...     if n < 2:
...             return n
...     return fibonacci(n-1) + fibonacci(n-2)
... 
>>> fibonacci(100)
354224848179261915075L

And retrieve the cache:

>>> fibonacci.cache
{(32,): 2178309, (23,): 28657, ... }

You can then pickle/unpickle the cache as you please and load it with:

fibonacci.cache = pickle.load(cache_file_object)

---

I found a feature request in python's issue tracker to add dumps/loads to lru_cache, but it wasn't accepted/implemented. Maybe in the future it will be possible to have built-in support for these operations via lru_cache.

You can use a library of mine, mezmorize

import random
from mezmorize import Cache

cache = Cache(CACHE_TYPE='filesystem', CACHE_DIR='cache')


@cache.memoize()
def add(a, b):
    return a + b + random.randrange(0, 1000)

>>> add(2, 5)
727
>>> add(2, 5)
727