Limited size dictionar with Random Eviction

redict.py

from random import randint


class REDict(dict):

    def __init__(self, maxsize, *args, **kwargs):
        self._maxsize = maxsize
        self._keys = []
        self._evict_cb = kwargs.pop('_evict_cb', None)
        dict.__init__(self, *args, **kwargs)

    def __setitem__(self, key, val):
        if len(self._keys) >= self._maxsize:
            i = randint(0, self._maxsize - 1)
            old_k = self._keys[i]
            old_v = self.pop(old_k)
            if self._evict_cb:
                self._evict_cb(old_k, old_v)
            self._keys[i] = key
        else:
            self._keys.append(key)
        dict.__setitem__(self, key, val)