# -*- coding: utf-8 -*-

import os

def alter(file,old_str,new_str,new_file_name):

    """

    将替换的字符串写到一个新的文件中

    """

    with open(file, "r") as f1,open("%s.bak" % file, "w") as f2:

        for line in f1:

            if old_str in line:

                line = line.replace(old_str, new_str)

            f2.write(line)

    os.rename("%s.bak" % file, new_file_name)

#将DPS.train文件中的__label__3替换为__label__2，生成新的文件叫DPS_new.train

alter("DPS.train", "__label__3", "__label__2","DPS_new.train")