"""
元 - meta
元数据 - 描述数据的数据 - metadata
元类 - 描述类的类 - metaclass - 继承自type
"""
import threading
class SingletonMeta(type):
"""自定义元类"""
def __init__(cls, *args, **kwargs):
cls.__instance = None
cls.lock = threading.Lock()
super().__init__(*args, **kwargs)
def __call__(cls, *args, **kwargs):
if cls.__instance is None:
with cls.lock:
if cls.__instance is None:
cls.__instance = super().__call__(*args, **kwargs)
return cls.__instance
class President(metaclass=SingletonMeta):
"""总统(单例类)"""
def __init__(self, name, country):
self.name = name
self.country = country
def __str__(self):
return f'{self.country}: {self.name}'
def main():
"""主函数"""
p1 = President('特朗普', '美国')
p2 = President('奥巴马', '美国')
p3 = President.__call__('克林顿', '美国')
print(p1 == p2)
print(p1 == p3)
print(p1, p2, p3, sep='\n')
if __name__ == '__main__':
main()
