test.py

class RingBuffer(object):
    def __init__(self, data):
        self._data = data

    def __getitem__(self, i):
        return self._data[i % len(self)]

    def __setitem__(self, i,v):
        self._data[i % len(self)] = v

    def __len__(self):
        return len(self._data)

def fib(n):
    rb = RingBuffer([1,1])
    for i in range(2,n):
        rb[i] = rb[i-1] + rb[i-2]

    return rb[n-1]