from itertools import dropwhile, takewhile, islice

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

for x in fibs():
    print(x)
    if x > 250:
        break

print(list(islice(fibs(), 15)))
print(list(takewhile(lambda x: x < 250, \
           dropwhile(lambda x: x < 8, fibs()))))