文件-重构代码

def solve():
    import json
    def get_stored_username():
        try:
            with open(____) as f:
                return json.load(____)
        except FileNotFoundError:
            return None
    def greet_user():
        username = get_stored_username()
        if username:
            print(____)
        else:
            print(____)
    with open(____) as f:
        json.dump(____)
    greet_user()