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


def sozdanie():
    filename = 'polzovatel.json'
    username = input('Введите ваше имя: ')
    with open(filename, 'w') as file:
        json.dump(username,file)
        return username


def vivod():
    a = privestvie()
    if a:
        print('С возвращением, ' + a )
    else:
        a = sozdanie()
        print('Мы вас запомнили, ' + a)
vivod()