懒加载代理模式

正常加载初始化实例

import time
class Test:
    def __init__(self):
        self.x = 'foo'
        self.y = 'bar'
        self._resource = self.resource()

    def resource(self):
        # 初始化中耗时操作
        print('初始化属性_resource......耗时5秒')
        time.sleep(5)
        _ = tuple(range(5))
        return _

if __name__ == '__main__':
    t = Test()
    print(t.x)
    print(t.y)
    print(t._resource)

输出结果:

初始化属性_resource......
foo
bar
(0, 1, 2, 3, 4)

在实例初始化后需要调用属性再加载

import time


class LazyProperty:
    def __init__(self, method):
        print('LazyProperty')
        self.method = method
        self.method_name = method.__name__

    def __get__(self, instance, owner):
        if not instance:  # 类调用
            return None
        value = self.method(instance)
        if __name__ == '__main__':  # 在主模块调用时每个实例有一个副本
            setattr(instance.__class__, self.method_name, value)
        else:  # 被其他模块调用时每个实例共用一个副本
            setattr(instance,self.method_name,value)
        return value


class Test:
    def __init__(self):
        self.x = 'foo'
        self.y = 'bar'
        self._resource = None

    @LazyProperty  # init_resource =LazyProperty(init_resource) 调用属性时执行__get__
    def init_resource(self):
        # 初始化中耗时操作
        print('初始化属性_resource......')
        time.sleep(5)
        self._resource = tuple(range(5))
        return self._resource


if __name__ == '__main__':
    t = Test()
    print(t.x)
    print(t.y)
    print(Test.init_resource)  # 类调用类属性时不会初始化返回None
    print(t.init_resource)  # 初始化返回初始化结果
    print(t._resource)

输出结果:

LazyProperty
foo
bar
None
初始化属性_resource......耗时5秒
(0, 1, 2, 3, 4)
(0, 1, 2, 3, 4)