#10-11 喜欢的数字：编写一个程序，提示用户输入他喜欢的数字，并使用
#json.dump()将这个数字存储到文件中。再编写一个程序，从文件中读取这个值，并打
#印消息“I know your favorite number! It’s _____.”。

def sorted_favourite_num():
    file_1 = 'favourite_num.json'
    num = input('enter one you favourite number: ')
    with open(file_1,'w') as file_ojt:
        json.dump(int(num),file_ojt)

def read_num():
    with open('favourite_num.json') as file_obj:
        num = json.load(file_obj)
        print("I know your favorite number! It’s {}".format(num))

sorted_favourite_num()
read_num()

10-12 记住喜欢的数字：将练习 10-11 中的两个程序合而为一。如果存储了用户喜 欢的数字，就向用户显示它，否则提示用户输入他喜欢的数字并将其存储到文件中。运 行这个程序两次，看看它是否像预期的那样工作

def sorted_favourite_num():
    file_1 = 'favourite_num.json'
    try:
        with open(file_1) as file_obj:
            num = json.load(file_obj)
    except FileNotFoundError:
        return None
    else:
        return num

def get_new_num():
    num = input('enter one you favourite number: ')
    file_1 = 'favourite_num.json'
    with open(file_1,'w') as file_ojt:
        json.dump(int(num),file_ojt)
    return num

def read_num():
    num = sorted_favourite_num()
    if num:
        print("I know your favorite number! It’s {}".format(num))
    else:
        num = get_new_num()
        print("I know your favorite number! It’s {}".format(num))


read_num()

10-13 验证用户：最后一个 remember_me.py 版本假设用户要么已输入其用户名，要么是首次运行该程序。我们应修改这个程序，以应对这样的情形：当前和最后一次运行 该程序的用户并非同一个人。 为此，在 greet_user()中打印欢迎用户回来的消息前，先询问他用户名是否是对的。 如果不对，就调用 get_new_username()让用户输入正确的用户名

import json

def get_stored_username():
    filename = 'username.json'
    try:
        with open(filename) as file_obj:
            username = json.load(file_obj)
    except FileNotFoundError:
        return None
    else:
        return username

def get_new_username():
   username = input("What is your name? ")
   filename = 'username.json'
   with open(filename, 'w') as f_obj:
      json.dump(username, f_obj)
   return username

def greet_user():
   username = get_stored_username()
   if username:
      y_n = input('Is ' + username + ' your name?(y/n)')
      if  y_n == 'y':
         print("Welcome back, " + username + "!")
      else:
         username = get_new_username()
         print("We'll remember you when you come back, " + username + "!")
   else:
      username = get_new_username()
      print("We'll remember you when you come back, " + username + "!")
greet_user()