code：

f = open('yesterday','r',encoding='utf-8')
f2 = open('yesterday.bak','w',encoding='utf-8')
old_str = input('请输入要修改的字符：')
replace_str = input('请输入替换成的字符:')
for line in f.readlines():
    line = line.replace(old_str,replace_str)
    print(line)
    f2.write(line)
f.close()
f2.close()

文件内容：（yesterday）

Somehow, it seems the love I knew was always the most destructive kind
不知为何，我经历的爱情总是最具毁灭性的的那种
Yesterday when I was young
昨日当我年少轻狂
The taste of life was sweet
生命的滋味是甜的
As rain upon my tongue
就如舌尖上的雨露

 

感想：

　　思路很简单就是打开源文件，然后循环，把源文件要替换的内容替换再写入新文件！