#Filename: file_read_and_write.py

 #打开文件，cNames读取所有行，储存在列表中，循环对每一行在起始处加上序号1，2，3，4

 with open(r'file/companies.txt') as f1:

     cNames = f1.readlines()

     for i in range(0,len(cNames)):

         cNames[i] = str(i+1) + '.' + '' + cNames[i]

 #将处理过的cNames写入新的文件中

 with open(r'file/scompanies.txt','w') as f2:

     f2.writelines(cNames)

google

tencent

alibaba

baidu

1.google

2.tencent

3.alibaba

4.baidu