from functools import wraps
def singleton(cls):
    """装饰类的装饰器"""
    instances = {}

    @wraps(cls)
    def wrapper(*args, **kwargs):
        if cls not in instances:
            instances[cls] = cls(*args, **kwargs)
        return instances[cls]

    return wrapper
@singleton
class President():
    """总统(单例类)"""
    pass