Default values in kwargs with class inheritance

Question

I have two classes A and B(A). Their constructor accept the style dictionary as a keyword argument.

For A objects I want, by default, the string green to be associated to style['color'].

For B objects color defaults to red.

I came up with this solution but find it rather clumsy. Is there a more elegant way to do this?

class A:
    def __init__(self, **kwargs):
        style = kwargs.pop('style', {})
        if 'color' not in style:
            style['color'] = 'green'
        print(style)

class B(A):
    def __init__(self, **kwargs):
        style = kwargs.pop('style', {})
        if 'color' not in style:
            style['color'] = 'red'
        super().__init__(style=style, **kwargs)

A()  #  {'color': 'green'}
B()  #  {'color': 'red'}
B(style={'color': 'blue'})  #  {'color': 'blue'}

Answer 1

Try the following instead.

It introduces a helper method to the base class called default_kwarg.

This can be called in both cases (superclass and subclass) to set the default value of the color key.

This approach also enables the style dict to contain other key/value pairs. I've added an extra example at the end that demonstrates this.

class A:
    def default_kwarg(self, arg, default):
        arg = arg.pop('style', {})
        if 'color' not in arg:
          arg['color'] = default
        return arg

    def __init__(self, **kwargs):
        style = self.default_kwarg(kwargs, 'green')
        print(style)

class B(A):
    def __init__(self, **kwargs):
        kwargs['style'] = self.default_kwarg(kwargs, 'red')
        super().__init__(**kwargs)

A()  #  {'color': 'green'}
B()  #  {'color': 'red'}
B(style={'color': 'blue'})  #  {'color': 'blue'}
B(style={'something': 'else'})  #  {'something': 'else', 'color': 'red'}

You could also generalize this helper method quite easily to apply defaults to other keys in the dict.