gistfile1.py

from itertools import islice

def fib_gen():
    a, b = 0, 1
    while 1:
        yield a
        a, b = b, a + b

assert [0, 1, 1, 2, 3, 5, 8] == list(islice(fib_gen(), 7))

def ftake(fnext, last):
    return [fnext() for	_ in xrange(last)]

def fib_gen2():
    global a; a = 1
    global b; b = 1
    def next():
        global a; global b;
        r = a
        a, b = b, a + b
        return r
    return next

assert [1,1,2,3,5] == ftake(fib_gen2(), 5)

class fib_gen3:
    def __init__(self):
        self.a, self.b = 1, 1

    def __call__(self):
        r = self.a
        self.a, self.b = self.b, self.a + self.b
        return r

assert [1,1,2,3,5] == ftake(fib_gen3(), 5)