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