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))

from itertools import chain

a = [1, 2]
b = (x for x in [3, 4])

c = chain(a, b)
print(list(c))

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()))