fibonacci.py

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

hofstadter.py

# Hofstadter Figure-Figure sequences
# F(1) = 1, S(1) = 2
# F(n) = F(n - 1) + S(n - 1)
def fig():
    f, s = 1, 2
    used = []
    while True:
        yield f, s
        f = f + s
        used.append(f)
        s += 1
        if used[0] == s:
            s += 1
            used = used[1:]