生成器

# 生成器与return的区别：
# return只能返回一次值，yield可以返回多次值
# yield到底做了什么？
# yield把函数变成生成器---》迭代器

from collections import Iterator
# 生成器就是一个函数，这个函数包含yield这个关键字
# def test():
#     print("first")
#     yield 1 #return 1
#     print("second")
#     yield 2
#
# g=test()
# print(g)
# # 看看是不是迭代器
# print(isinstance(g,Iterator))
#
# print(next(g))
# print(next(g))

# next(g) # 没有1输出是因为没有发返回值保存下来
# next(g)

# for i in g:
#     next(i)

def countdown(n):
    print('start countdown')
    while n>0:
       yield n
       n-=1
    print('done')

g=countdown(5)
# print(g)
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))
# print(next(g))
# next(g)

for i in g:
    print(i)

while True:
    try:
        print(next(g))
    except StopIteration:
        break

while True:
    try:
        print(next(g))
    except StopIteration:
        break

# 在nginx下,写下面的命令，可以得到文件内的内容
tail -f /var/log/nginx/access.log

echo 'hoeel' >> /var/log/nginx/access.log

 

# /user/bin/env python
import time
def tail(file_path):
    with open(file_path,'r') as f:
        f.seek(0,2)
            line=f.readline()
            if not line:
                time.sleep(0.3)
                print("=======>")
                continue
            else:
                # print(line,end='')
                yield line

# g=tail('a.txt')
# print(g)
# print(next(g))

# 要打印带error那行：
def grep(pattern,lines):
    for line in lines:
        if pattern in line:
            print('33[45m%s33[0m' %line)

g=tail('a.txt')
grep('error',g)