There is a bug in the fibonacci example: it sums odd numbers instead of even. from itertools import takewhile def ifibonacci(a=1, b=1): while True

There is a bug in the fibonacci example: it sums odd numbers instead of even. from itertools import takewhile def ifibonacci(a=1, b=1): while True: yield a a, b = b, a + b candidates = takewhile(lambda n: n < 4000000, ifibonacci()) print sum(n for n in candidates if n % 2 == 0)