diy.py

with open(r'/Users/xujunheng/Desktop/sales_list.txt','r',encoding='UTF-8')as file:
    a=file.readlines()
    #print(a)
new=[]
for i in a:
    data=i.split()
    sum=0
    for sales in data[1:]:
        sum=sum+int(sales)
    S=data[0]+str(sum)+'\n'
    new.append(S)
    #print(S)
with open(r'/Users/xujunheng/Desktop/new_sales_list.txt','a',encoding='UTF-8')as file:
    file.writelines(new)