memoize.py

class Memoizer(object):
    """Memoizer for pure functions with positional hashable arguments.

    Eviction from cache is done more or less at random, which
    in practice is surprisingly close to a LRU strategy.
    """

    def __init__(self, func, maxsize=10000):
        self.func = func
        self.maxsize = maxsize
        self.vals = {}
        self.keys = set()

    def __call__(self, *args):
        try:
            return self.vals[args]
        except KeyError:
            pass

        # evict
        if len(self.keys) > self.maxsize:
            del self.vals[self.keys.pop()]

        # calc val and add to cache
        val = self.func(*args)
        self.vals[args] = val
        self.keys.add(args)
        return val