Making this reduce() Fibonacci generator better
A reduce (that's it, a fold) is not exactly the abstraction for the task (what input collection are you going to fold here?). Anyway, you can cheat a little bit and fold the indexes even if you don't really use them within the folding function. This works for Python 2.x:

def next_fib((x, y), n):
    return (y, x + y)

reduce(next_fib, xrange(5), (1, 1))[0]
#=&gt; 8