greenlet

from greenlet import greenlet
import time
def t1():
    while True:
        print("————A————")
        gr2.switch()
        time.sleep(3)
def t2():
    while True:
        print("————B————")
        gr2.switch()
        time.sleep(2)

gr1=greenlet(t1)
gr2=greenlet(t2)
gr1.switch()