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GitHub Repository: jackfrued/Python-100-Days
 Path: blob/master/Day16-20/code/example10.py
Views: 729
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"""

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装饰类的装饰器 - 单例模式 - 一个类只能创建出唯一的对象

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上下文语法：

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__enter__ / __exit__

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"""

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import threading

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from functools import wraps

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def singleton(cls):

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    """单例装饰器"""

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    instances = {}

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    lock = threading.Lock()

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    @wraps(cls)

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    def wrapper(*args, **kwargs):

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        if cls not in instances:

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            with lock:

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                if cls not in instances:

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                    instances[cls] = cls(*args, **kwargs)

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        return instances[cls]

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    return wrapper

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@singleton

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class President():

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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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    print(President.__name__)

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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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    print(p1 == p2)

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    print(p1)

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    print(p2)

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if __name__ == '__main__':

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    main()

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