naive async flow like node, using promise

promise.py

import signal

# broken in eventloop things
class Promise:
    def __init__(self, f):
        self.status = 'PENDING'
        self.cb = None
        f(self.__resolve)

    def resolve(v):
        if isinstance(v, Promise):
            return v
        else:
            return Promise(lambda res:res(v))

    def __resolve(self, v):
        self.status = 'RESOLVED'
        if self.cb:
            Promise.resolve(self.cb(v))
        else:
            self.value = v

    def then(self, cb):
        if self.status == 'PENDING':
            self.cb = cb
        else:
            return Promise.resolve(cb(self.value))

def run(gen, v=None):
    try:
        ret = gen.send(v)
        ret.then(lambda res: run(gen, res))
    except StopIteration as e:
        print('gen done')

def sleep(n):
    def f(resolve):
        signal.signal(signal.SIGALRM, lambda signum, frame: resolve('wake up'))
        signal.setitimer(signal.ITIMER_REAL, n)

    return Promise(f)

def fakeAjax():
    ret = yield sleep(1)
    print(f'after sleep1: {ret}')
    ret2 = yield sleep(1)
    print(f'after sleep2: {ret2}')
    
if name == '__main__':
    run(fakeAjax())
    print('first one')

# first one
# after sleep1: wake up
# after sleep2: wake up
# gen done