import json


class Config():
    def __init__(self, filename):
        self.filename = filename

    def load(self):
        try:
            with open(self.filename, "r", encoding="utf-8") as file:
                return json.load(file)
        except FileNotFoundError:
            return {}

    def save(self, data):
        with open(self.filename, "w", encoding="utf-8") as file:
            json.dump(data, file,indent=4, ensure_ascii=False)

    def get(self, key, default=None):
        data = self.load()
        return data.get(key, default)


    def set(self, key, value):
        data = self.load()
        data[key]=value
        self.save(data)


class Application():
    def __init__(self, config):
        self.config = config

    def run(self):
        username = self.config.get("username","гость")
        print(f"Hello,{username}")

    def set_username(self, name):
        self.config.set("username", name)

config = Config("settings.json")
ap = Application(config)
ap.set_username("Иван")
ap.run()