Python Mixins：*args/**kwargs vs 显式调用`__init__`

Question

I try to write an example of Mixins using Clickable and Rectangle classes, which are superclasses of the Button class.

Currently I use:

class Clickable:
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.clicks = 0

    def click(self):
        self.clicks = self.clicks + 1


class Rectangle:
    def __init__(self, x0, y0, x1, y1, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.upper_right = (x0, y0)
        self.lower_down = (x1, y1)


class Button(Clickable, Rectangle):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

But I consider using:

class Clickable:
    def __init__(self):
        self.clicks = 0

    def click(self):
        self.clicks = self.clicks + 1


class Rectangle:
    def __init__(self, x0, y0, x1, y1):
        self.upper_right = (x0, y0)
        self.lower_down = (x1, y1)


class Button(Clickable, Rectangle):
    def __init__(self, x0, y0, x1, y1):
        Rectangle.__init__(self, x0, y0, x1, y1)
        Clickable.__init__(self)

Is one of them is better for some reason?

Answer 1

The recommended way (see https://rhettinger.wordpress.com/2011/05/26/super-considered-super/ ) is to use keyword arguments to avoid conflicts between which parent is expected to be passed which positional arguments.

class Clickable:
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.clicks = 0

    def click(self):
        self.clicks = self.clicks + 1


class Rectangle:
    def __init__(self, x0, y0, x1, y1, **kwargs):
        super().__init__(**kwargs)
        self.upper_right = (x0, y0)
        self.lower_down = (x1, y1)


class Button(Clickable, Rectangle):
    # No need to override __init__ if all it does
    # is pass all its arguments to the next invocation
    pass


b = Button(x0=0, y0=0, x1=10, y1=10)

Remember, the reason for accepting arbitrary keyword arguments and passing them on in the first place is that you don't know which class super() will produce, so you can't predict the expected signature.

Mixins are nearly, by definition, expected to support cooperative inheritance, because they are expected to be used with multiple inheritance and someone will probably want to use your mixin in a class that does.