Python: yield from

import time


def dubious():
    print(f"\033[32;40;7m{'dubious start'}\033[0m")
    while True:
        send_value = yield
        if send_value is None:
            break
        commence = time.time()
        time.sleep(send_value)

    print('in dubious', time.time() - commence)
    # print('in dubious')
    return time.time() - commence
    # return 'return from dubious'


def grouper():
    while True:
        yield_from_value = yield from dubious()
        print('in grouper', yield_from_value)


g = grouper()
print('{0} {1} {0}'.format('~' * 20, 1))
print('next1 =', next(g))
print('{0} {1} {0}'.format('~' * 20, 2))
print('next2 =', g.send(2))
print('{0} {1} {0}'.format('~' * 20, 3))
print('next3 =', g.send(None))
print('{0} {1} {0}'.format('~' * 20, 4))
print('next4 =', g.send(None))

# grouper 死循环，每一次循环都会生成一个新的dubious generator，不断从dubious generator取值，最后捕获StopIteration，把dubious generator的StopIteration的异常 exc.value赋值给yield_from_value
# 此时，grouper的第一轮循环结束，再次进入while True循环，进行相同过程