python 协程 gevent

import gevent

def f1():
    print("print in f1")
    gevent.sleep(2)
    print("switch to foo again")
def f2():
    print("print in f2")
    gevent.sleep(1)
    print("switch to f2 again")
def f3():
    print("print in f3")
    gevent.sleep(0)
    print("switch to f3 again")
gevent.joinall([
    gevent.spawn(f1),
    gevent.spawn(f2),
    gevent.spawn(f3)
])

'''result:
        print in f1
        print in f2
        print in f3
        switch to f3 again
        switch to f2 again
        switch to foo again
'''