least_used.py

import operator


class LeastUsed(object):
    """
    Class that stores a list of items.

    When an item is requested, that item is considered to have been 'used'

    Each time an item is requested, request the one that has been used the least.

    """

    def __init__(self, items):
        self.items = {item: 0 for item in items}

    @property
    def next_item(self):
        return sorted(self.items.items(), key=operator.itemgetter(1))[0]

    @property
    def get(self):
        key, _ = self.next_item
        self.items[key] += 1
        return key

Note: do not use this -- use itertools.cycle ¯_(ツ)_/¯