def collect(n, acc=[]):
    acc.append(n)
    if n == 0:
        return acc
    return collect(n - 1, acc)

print(collect(2), collect(1))

a = [10, 20, 30]
b = [1, 2]

for i, j in zip(enumerate(a), b):
    print(i, j)

class Counter:
    def __init__(self, start, stop):
        self.current = start
        self.stop = stop

    def __iter__(self):
        return self

    def __next__(self):
        if self.current >= self.stop:
            raise StopIteration
        result = self.current
        self.current += 1
        return result

c = Counter(3, 5)
print(list(c))
print(list(c))

def gen():
    yield 1
    yield 2
    return 3

g = gen()
print(list(g))

def trace():
    print("start")
    yield 1
    print("middle")
    yield 2
    print("end")
g = trace()
a = next(g)
b = next(g)

gen = (x * 2 for x in range(3))
print(sum(gen) + sum(gen))

outer = (x for x in range(3))
inner = (y * 10 for y in outer if y % 2 == 0)

print(list(inner))
print(list(outer))

def gen1():
    yield from [1, 2]
    yield 3

print(list(gen1()))

def sub():
    yield 1
    yield 2

def main():
    yield 0
    yield from sub()
    yield 3

g = main()
print(next(g), next(g), next(g), next(g))