修改文件内容--初学很low的写法

import os
f = open('yy.txt','r',encoding='utf-8')
f_new = open('yy.bak','w+',encoding='utf-8')
for line in f:
    if '小光头' in line:
        line = line.replace('小光头','大头仔')
    f_new.write(line)
f.close()
f = open('yy.txt','w',encoding='utf-8')
f_new.seek(0)
for line_new in f_new:
    f.write(line_new)
f.close()
f_new.close()