Python：多重继承，拷贝构造函数，class初始化和()重载

Question

我一直在寻找一种方法来初始化派生的 class，就像在 C++ 中一样使用复制构造函数和 () 运算符

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，如果我有一个 class 派生自它自己的其他两个加成员并想出以下内容，我将如何实现这种初始化方式：

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}

所以我想知道这在多大程度上是非 pythonic 方式？如果有更好的方法（或没有办法）做同样的事情？

Answer 1

好吧，您不想创建一个实例来创建一个新实例，所以您可能想要 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 中所做的那样。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')

真的，我更喜欢这样，现在我不必担心破坏值或其他怪异现象。

如果你真的想要快捷方式，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少"clever"经常"better"

Python：多重继承，拷贝构造函数，class初始化和()重载

Python: multiple inheritance, copy constructor, class initialization and () overloading

python

multiple-inheritance

copy-constructor

in-class-initialization