rangeset.py

class Cached(object):
    """Cache classes with positional arguments."""
        
    _cache = {}

    def __new__(cls, *args):
        if args not in cls._cache:
            cls._cache[args] = super(Cached, cls).__new__(cls)
        return cls._cache[args]
        

class RangeSet(Cached):
    """RangeSet([start,] stop [, step]) -> cross between range and set"""

    def __init__(self, *args):
        self._list = range(*args)
        self._set = frozenset(self._list)
        if len(args) == 1:
            self._start, self._stop, self._step = 0, args[0], 1
        elif len(args) == 2:
            self._start, self._stop = args
            self._step = 1
        else:
            self._start, self._stop, self._step = args

    @property
    def start(self):
        return self._start

    @property
    def stop(self):
        return self._stop

    @property
    def step(self):
        return self._step
            
    def __contains__(self, value):
        return value in self._set

    def __eq__(self, other):
        try:
            return self._set == other._set
        except AttributeError:
            return self._set == other
            
    def __getitem__(self, index):
        return self._list[index]

    def __hash__(self):
        return hash(self._set)

    def __iter__(self):
        return iter(self._list)

    def __repr__(self):
        return 'RangeSet({0.start}, {0.stop}, {0.step})'.format(self)