recursive persistent memoization with python

shelve_recursive_memoization.py

import shelve
import functools


def cache(filename):
    def decorating_function(user_function):
        def wrapper(*args, **kwds):

            key = str(hash(functools._make_key(args, kwds, typed=False)))

            if not hasattr(cache, '_shelve'):
                cache._shelve = shelve.open(filename, writeback=True)
                should_close_shelve = True
            else:
                should_close_shelve = False

            try:
                return cache._shelve[key]
            except KeyError:
                result = user_function(*args, **kwds)
                cache._shelve[key] = result
                return result

            if should_close_shelve:
                self._shelve.close()
                del self._shelve
            else:
                self._shelve.sync()

        return functools.update_wrapper(wrapper, user_function)

    return decorating_function