发送值到生成器

def mygen():
    a=5
    while True:
        f=(yield a)
        if f is not None:
            a=f

>>> g = mygen()
>>> g.next()
5
>>> g.next()
5
>>> g.send(7)  #we send this back to the generator
7
>>> g.next() #now it will yield 7 until we send something else
7