字典循环

users = {
"niuhanyang":'123456sdf',
"niuhanyang2":'123456sd',
"niuhanyang3":'123456sdf',
"niuhanyang4":'1234sdf56',
"niuhanyang5":'12345gsdfs6',
"niuhanyang6":'1234324g56',
}

#、把字典里面每个用户的密码，前面都加上 username_ +

#1、循环这个字典
#2、把value修改成value = key_+value
# for k in users:#直接循环一个字典的话，循环的是key
# value = users[k] #通过key取到value
# users[k] = '%s_%s'%(k,value)
# print(users)