Question

我一直在寻找一种使用复制构造函数和（）运算符初始化派生类的方法，就像在C ++中一样

class Rectangle {
    int width, height;
  public:
    Rectangle (int,int);
    int area () {return (width*height);}
};

Rectangle::Rectangle (int a, int b) {
  width = a;
  height = b;
}

r = Rectangle(2,3)
s = Rectangle(r) /* <--using copy constructor to initialize*/

然后我在想如何实现这种初始化方式，以防我有一个派生自其他两个以上成员的类，并提出以下内容：

class MyBase1(object):
    def __init__(self, *args, **kwargs):
        self.x = kwargs.get('x')
        self.y = kwargs.get('y')
        print("mybase1 {}".format(kwargs))

    def print_base1(self):
        pass


class MyBase2(object):
    def __init__(self, *args, **kwargs):
        self.s = kwargs.get('s')
        self.p = kwargs.get('p')
        print("mybase2 {}".format(kwargs))

    def print_base2(self):
        pass


class MyChild(MyBase1, MyBase2):

    def __init__(self, **kwargs):
        MyBase1.__init__(self, **kwargs)
        MyBase2.__init__(self, **kwargs)
        self.function_name = kwargs.get('function')


    def __call__(self, my_base1, my_base2, **kwargs):
        initialization_dictionary = dict(vars(my_base1), **vars(my_base2))
        initialization_dictionary = dict(initialization_dictionary, **kwargs)
        newInstance = MyChild(**initialization_dictionary)
        return newInstance

然后打电话：

base1 = MyBase1(x=1, y=2)
base2 = MyBase2(s=3, p=4)

child = MyChild()(base1, base2, function='arcsine') #<--initialising 

[stm for stm in dir(child) if not stm.startswith('__')]
# gives:['function_name', 'p', 'print_base1', 'print_base2', 's', 'x', 'y']

vars(child)
# gives:{'function_name': 'arcsine', 'p': 4, 's': 3, 'x': 1, 'y': 2}

所以我想知道这是多少非pythonic的方式？如果有更好的方式（或没有办法）做同样的事情？

Answer 1

嗯，您不想创建实例来创建新实例，因此您可能需要classmethod或staticmethod。这也不是使用__call__的地方。

我可能会这样做：

class MyChild(MyBase1, MyBase2):
    @classmethod
    def build_from_bases(klass, base1, base2, **kwargs):
        kwargs.update(base1.__dict__)
        # Note if base2 has values for x and y, they will clobber what was in base1
        kwargs.update(base2.__dict__)
        return klass(**kwargs)

但是使用Base1和Base2的实例来构建MyChild的实例并不像我在python中做的那样。更有可能使用明显的：

mychild = MyChild(x=base1.x, y=base1.y, s=base2.s, p=base2.p, function='foo')

我真的更喜欢这样，现在我不必担心破坏价值或其他奇怪。

如果你真的想要捷径方法，你可以将两者结合起来：

class MyChild(MyBase1, MyBase2):
    @classmethod
    def build_from_bases(klass, base1, base2, **kwargs):
       return klass(x=base1.x, y=base1.y, s=base2.s, p=base2.p, **kwargs)

在python less＆＃34;聪明＆＃34;经常＆＃34;更好＆＃34;

Python：多重继承，复制构造函数，类初始化和（）重载

1 个答案: