python-day17--Generator

1. Essence: Iterator

2. Generator function:

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 (ret) #取第三个值 An error because there is no third value

3. example of the generator listener file input

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 ()  # reads new lines of text in the file
            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 (), nothing like send and next effect
Print (avg.send)  #传值 Next
Print (Avg.send (20))

5. Transfer value:

#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 [+ +]
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--Generator