# fibonacci.second.py
def fibonacci(N):
    """Return all fibonacci numbers up to N. """
    yield 0
    if N == 0:
        return
    a = 0
    b = 1
    while b <= N:
        yield b
        a, b = b, a + b


print(list(fibonacci(0)))   # [0]
print(list(fibonacci(1)))   # [0, 1, 1]
print(list(fibonacci(50)))  # [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]