#coding:gbk
import json

def get_stored_username():
	'''如果存储了用户名,就获取它'''
	filename = 'username.json'
	try:
		with open(filename) as obj:
			username = json.load(obj)
	except FileNotFoundError:
		return None
	else:
		return username
		
def get_new_username():
	'''提示用户输入用户名'''
	username = input('what U name? \n\tInput you name : ')
	filename = 'username.json'
	with open(filename,'w') as obj:
		json.dump(username,obj)
	return username
	
def greet_user():
	'''问候用户,并指出其姓名'''
	username = get_stored_username()
	i = input('\nAre U name is :'+username+'\n\ty/n : ')
	if i == 'y':
		print('欢迎回来, '+username)
	
	else:
		username = get_new_username()
		print('we`ll remember u ,when u come back, '+username+'!')

greet_user()