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()))

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

from contextlib import contextmanager

@contextmanager
def simple_context():
    print("enter")
    yield
    print("exit")

with simple_context():
    print("inside")

 echo():
    value = yield "start"
    yield value

g = echo()
print(next(g))
print(g.send("hello"))

def flatten(lst):
    for item in lst:
        if isinstance(item, list):
            yield from flatten(item)
        else:
            yield item

print(list(flatten([1, [2, [3, 4]], 5])))

from itertools import tee

it = iter([10, 20, 30])
a, b = tee(it)

print(next(a), next(b), list(a), list(b))

with open("data.txt", "w", encoding="utf-8") as f:
    f.write("apple\n")
    f.write("banana\n")
    f.write("cherry\n")

def read_lines():
    for line in open("data.txt"):
        yield line.strip()

lines = read_lines()
print(next(lines))
print(next(lines))
print(next(lines))