python-day17--產生器

標籤：檔案輸入   adl   lin   next   log   code   報錯   time   效果   

1.本質：就是迭代器

2.產生器函數：

def func():
    a=1
    b=2
    yield a    #返回第一個值
    yield b    #返回第二個值

ret = func()  #拿到一個產生器
print(next(ret)) #取第一個值
print(next(ret)) #取第二個值
print(next(ret)) #取第三個值 會報錯 因為沒有第三個值

3.產生器監聽檔案輸入的例子

import time
def tail(filename):
    with open(filename) as f:
        f.seek(0, 2) #從檔案末尾算起
        while True:
            line = f.readline()  # 讀取檔案中新的文本行
            if not line:
                time.sleep(0.1)
                continue
            yield line

print(next(tail(‘tmp_file‘)))

4.#計算移動平均值

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)  #啟用產生器 avg.send(),什麼都不send和next效果一樣
print(avg.send(10))  #傳值 next
print(avg.send(20))

5.傳值：

#計算移動平均值
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--產生器