用字典创建一个平台的用户信息（包含用户名和密码）管理系统，新用户可以用与现有系统帐号不冲突的用户名创建帐号，已存在的老用户则可以用用户名和密码登陆重返系统。

user = {'Wangerxiao':123456,'Wangdachui':456789,'Wangxiaochui':789123}
def newusers(name):
if name in user.keys():
print("your name is already exist,please try new one...")
name = input("please input your info_Name:\n")
newusers(name)
else:
user[name] = input("please set your password:")

print('Welcome',name)
def oldusers(username,password):
if int(password) == user[username]:
print(username,'Welcome back!')
else:
print('Login incorrect!')
def showSets():
for k,v in user.items():
print(k,v)

def login():
N = 'New User Login'
O = 'Old User Login'
E = 'Exit'
S = 'Show the userSets'
option = input('You are:New User Login or Old user Login or Exit or ShowSets?( N/O/E/S:)')
if option == 'N':
name = input('Please input your name:')
newusers(name)
elif option == 'O':
username = input('name:')
password = input('passowrd:')
oldusers(username,password)
elif option == 'E':
print('BYE...')
elif option =='S':
showSets()
else:
print("Input Error...\n+++++++++++++ try again ++++++++++++")

if __name__ == '__main__':
print('''
+++++++++++++ the UserSets practise +++++++++++++\n
+++++++++++++ @LucifulSP  2018/2/18    +++++++++++++
''')
login()