I'm using @functools.lru_cache
in Python 3.3. I would like to save the cache to a file, in order to restore it when the program will be restarted. How could I do?
Edit 1 Possible solution: We need to pickle any sort of callable
Problem pickling __closure__
:
_pickle.PicklingError: Can't pickle <class 'cell'>: attribute lookup builtins.cell failed
If I try to restore the function without it, I get:
TypeError: arg 5 (closure) must be tuple
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 wrapsdef 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
.