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