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GitHub Repository: jackfrued/Python-100-Days
 Path: blob/master/Day16-20/code/example17.py
Views: 729
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"""

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多重继承 - 一个类有两个或者两个以上的父类

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MRO - 方法解析顺序 - Method Resolution Order

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当出现菱形继承（钻石继承）的时候，子类到底继承哪个父类的方法

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Python 2.x - 深度优先搜索

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Python 3.x - C3算法 - 类似于广度优先搜索

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"""

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class A():

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    def say_hello(self):

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        print('Hello, A')

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class B(A):

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    pass

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class C(A):

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    def say_hello(self):

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        print('Hello, C')

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class D(B, C):

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    pass

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class SetOnceMappingMixin():

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    """自定义混入类"""

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    __slots__ = ()

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    def __setitem__(self, key, value):

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        if key in self:

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            raise KeyError(str(key) + ' already set')

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        return super().__setitem__(key, value)

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class SetOnceDict(SetOnceMappingMixin, dict):

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    """自定义字典"""

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    pass

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def main():

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    print(D.mro())

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    # print(D.__mro__)

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    D().say_hello()

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    print(SetOnceDict.__mro__)

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    my_dict= SetOnceDict()

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    my_dict['username'] = 'jackfrued'

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    my_dict['username'] = 'hellokitty'

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if __name__ == '__main__':

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    main()

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