生成器、迭代器脚本实例

def counter (start_at=0) :
    count = start_at
    while True:
        val = (yield count)        
        if val is not None:
            count = val
        else:
            count +=1

count = counter(5)   #建立一个生成器
print(count.__next__())  #向外面返回一个5，然后count 变为6
print(count.__next__())   #返回一个6
print(count.send(9))      #往yield后面传一个值
print(count.__next__())   
count.close()              #关闭这个生成器
print(count.__next__())    #不能在生成一个新的值了

执行结果：
5
6
9
10
  File "I:/untitled/cx/11月/11-6/2生成器函数.py", line 38, in <module>
    print(count.__next__())
StopIteration

 有?个数据结构如下所?，请编写?个函数从该结构数据中返回由指定的字段和对应的值组成的字 典。如果指定字段不存在，则跳过该字段。（10分）
 data:{"time":"2016-08-05T13:13:05",
 "some_id":"ID1234",
 "grp1":{    "fld1":1,
 "fld2":2},
 "xxx2":{    "fld3":0,
 "fld5":0.4},
 "fld6":11,
 "fld7":7,
 "fld46":8}
 fields:由"|"连接的以"fld"开头的字符串,如:fld2|fld3|fld7|fld19

 def  select(data,fields):
 TODO:implementation
return result

data= {"time":"2016-08-05T13:13:05","some_id":"ID1234","grp1":{    "fld1":1,"fld2":2},
          "xxx2":{    "fld3":0,"fld5":0.4},"fld6":11,"fld7":7,"fld46":8}
fields = "fld2|fld3|fld7|fld19"

第一种解法
def  select(data,fields):
    result = {}
    fields_lst = fields.strip().split(‘|‘)
    for m in data.keys():
        if m in fields_lst:
            result[m] = data[m]
        elif type(data[m]) == dict:
            for n in data[m].keys():
                if n in fields_lst:
                    result[n] = data[m][n]
    return result
print(select(data,fields))

第二种解法
def  select(data,fields):
    result = {}
    result_1={}
    fields_lst = fields.strip().split(‘|‘)
    for m in data.keys():
        if type(data[m]) == dict:
            for n in data[m].keys():
                result_1[n] = data[m][n]
        else:
            result_1[m] = data[m]
    for k in fields_lst:
        if k in result_1.keys():
            result[k] = result_1[k]
    return result
print(select(data,fields))

def averager():
    total = 0.0
    count = 0
    average = None
    while True:
        term = yield average
        total += term
        count += 1
        average = total/count


g_avg = averager()
next(g_avg)
print(g_avg.send(10))
print(g_avg.send(30))
print(g_avg.send(5))

import time


def tail(filename):
    f = open(filename)
    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

tail_g = tail(‘tmp‘)
for line in tail_g:
    print(line)

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))
print(list(g2))

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)    =》(add(10,i) for i in add(10,i) for i in [0,1,2,3])
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　这是一个生成器，在打印结果之前不会执行。

print(list(g))