even_fibs.py

from itertools import takewhile, ifilter

def fibs():
    fib0 = 1
    fib1 = 1
    while True:
        yield fib0
        newfib = fib0 + fib1
        fib0 = fib1
        fib1 = newfib

even_fibs = ifilter(lambda i: i % 2 == 0, fibs())

even_fibs_under_four_million = takewhile(lambda i: i < 4000000, even_fibs)

result = sum(even_fibs_under_four_million)

print result