使用json存储数据

import json
def get_stored_username():
    """如果获取了用户名，就获取她"""
    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():
    """提示用户输入用户名"""
    filename = 'username.json'
    username = input("Please input your name\n")
    with open(filename,'w') as file_obj:
        json.dump(username,file_obj)
        """写入数据，从左写入右"""
    return username
def greet_user():
    """问候用户"""
    username = get_stored_username()
    if username:
        print(username + "  Welcome back\n")
    else:
        username = get_new_username()
greet_user()