生成器

#题目一：
def my_range(start,stop,step=1):
    while start < stop:
        yield start
        start+=step

#执行函数得到生成器，本质就是迭代器
obj=my_range(1,7,2) #1  3  5
print(next(obj))
print(next(obj))
print(next(obj))
print(next(obj)) #StopIteration

#应用于for循环
for i in my_range(1,7,2):
    print(i)

import time
def tail(filepath):
    with open(filepath,‘rb‘) as f:
        f.seek(0,2)
        while True:
            line=f.readline()
            if line:
                yield line
            else:
                time.sleep(0.2)

def grep(pattern,lines):
    for line in lines:
        line=line.decode(‘utf-8‘)
        if pattern in line:
            yield line

for line in grep(‘404‘,tail(‘access.log‘)):
    print(line,end=‘‘)

#测试
with open(‘access.log‘,‘a‘,encoding=‘utf-8‘) as f:
    f.write(‘出错啦404\n‘)