def counter(name):

    print('%s ready to count'%name)

    num_list=[]

    while True: #这个语句的作用是循环利用yield，这样的话对象就可以无限传值了

        #yield前的变量是接收值的

        num=yield '现在的列表是%s'%num_list #yield后面的变量会打印处理

        num_list.append(num)

        print('%s start to count %s'%(name,num))

e=counter('xincheng')

print(e.send(None)) #或者 next(e)

print(e.send(''))

print(e.send(''))

for i in range(3,10):

    print(e.send(i))

xincheng ready to count

现在的列表是[]

xincheng start to count 1

现在的列表是['']

xincheng start to count 2

现在的列表是['', '']

xincheng start to count 3

现在的列表是['', '', 3]

xincheng start to count 4

现在的列表是['', '', 3, 4]

xincheng start to count 5

现在的列表是['', '', 3, 4, 5]

xincheng start to count 6

现在的列表是['', '', 3, 4, 5, 6]

xincheng start to count 7

现在的列表是['', '', 3, 4, 5, 6, 7]

xincheng start to count 8

现在的列表是['', '', 3, 4, 5, 6, 7, 8]

xincheng start to count 9

现在的列表是['', '', 3, 4, 5, 6, 7, 8, 9]

例子一结果

def counter(name):

    print('%s ready to count'%name)

    num_list=[]

    while True:

        num=yield num_list,'hehe' #yield后面的变量会答应处理，多个用，隔开，结果就会放入一个元组中

        num_list.append(num)

        print('%s start to count %s'%(name,num)) #yield后面的语句一般为下一个yield的开始

e=counter('xincheng')

next(e)

s=e.send('') #xincheng start to count 1

print(s,type(s)) #(['1'], 'hehe') <class 'tuple'> yield后面的东西是给对象传的值，多个值放在一个元组中

def gen1():

    for c in 'ab':

        yield c

    for i in range(3):

        yield i

print(list(gen1()))

def gen2():

    yield from 'ab'

    yield from range(3)

print(list(gen2()))

#两个print的值都为['a', 'b', 0, 1, 2]

def demo():

    for i in range(4):

        yield i

g=demo()

g1=(i for i in g)

g2=(i for i in g1)

print(list(g1))  #[0, 1, 2, 3]

print(list(g2))  #[]

#g是第一个生成器，g1取得值来自于g,g2取值来自于g1，归根到底还是g，list是可迭代对象，将g1赋予list得方法，其实是从g中取值，而且取完了，g2自然就是空值了

请看下面得变体

def demo():
    for i in range(4):
        yield i

g=demo()
g1=(i for i in g)
g2=(i for i in g1)
print(next(g)) # 0
print(next(g1)) # 1
print(next(g2)) # 2

def add(n,i):

    return n+i

def test():

    for i in range(4):

        yield i

g=test()

for n in [1,10]:

    g=(add(n,i) for i in g)

print(list(g))

#此例子的for循环中有两个元素，其结果为 [20, 21, 22, 23]

#如果将for循环下面得表达式换成g=[add(n,i) for i in g] 换成了【】，结果为[11, 12, 13, 14]

#如果将for循环的表达式换成 for n in [1,3,10]  或者 for n in [1,11,10] 都是三个元素，其结果为[30, 31, 32, 33]

#如果是 for n in [1,3,6,7,10,11,100,10]总共8个元素 其结果为[80, 81, 82, 83]