1.本质：就是迭代器

2.生成器函数：

def func():
    a=1
    b=2
    yield a    #返回第一个值
    yield b    #返回第二个值

ret = func()  #拿到一个生成器
print(next(ret)) #取第一个值
print(next(ret)) #取第二个值
print(next(ret)) #取第三个值 会报错 因为没有第三个值

3.生成器监听文件输入的例子

import time
def tail(filename):
    with open(filename) as f:
        f.seek(0, 2) #从文件末尾算起
        while True:
            line = f.readline()  # 读取文件中新的文本行
            if not line:
                time.sleep(0.1)
                continue
            yield line

print(next(tail(‘tmp_file‘)))

4.#计算移动平均值

def averager():
    total = 0
    day = 0
    avrage = 0
    while True:
        day_num  = yield avrage  #return avrage
        total += day_num
        day += 1
        avrage = total/day

avg = averager()
num = next(avg)  #激活生成器 avg.send(),什么都不send和next效果一样
print(avg.send(10))  #传值 next
print(avg.send(20))

5.传值：

#计算移动平均值
def wrap(func):

    def inner(*args,**kwargs):
        g = func(*args,**kwargs)
        next(g)
        return g
    return inner

@wrap
def averager():
    total = 0
    day = 0
    avrage = 0
    while True:
        day_num  = yield avrage  #return avrage
        total += day_num
        day += 1
        avrage = total/day

g = averager()
print(g.send(10))
print(g.send(20))

6.

def func():
    # for i in ‘AB‘:
    #     yield i
    yield from ‘AB‘
    yield from [1,2,3]
g = func()
l = []
l.append(next(g))
l.append(next(g))
l.append(next(g))
l.append(next(g))
l.append(next(g))
print(l)

python-day17--生成器