from itertools import cycle

c = cycle([10, 20])
out = []
for i, val in enumerate(c):
    if i >= 3:
        break
    out.append(val)

print(out)

def sub():
    for i in range(2):
        yield i

def main():
    yield -1
    for x in sub():
        yield x
    yield 2

print(list(main()))

g = (x for x in range(2))
print(next(g), next(g), next(g, 99))