模拟管道，实现功能:tail -f access.log | grep '404'

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(0.05)

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


lines=grep(tail('access.log'),'404')

for line in lines:
    print(line)