python-day17--生成器

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 timedef 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 nextprint(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

@wrapdef 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)