Python class inheritance with changing default values

Question

I have few classes that have same props and it will be much more of them so how I can make other class to pass that common props to each class but to use default values from Props class if I do not want to enter some of the arguments. So far if I do not enter anchor, layer or linetype_scale argument I am getting error TypeError: __init__() missing 3 required positional arguments: 'anchor', 'layer', and 'linetype_scale'.

class Props():
    def __init__(self, anchor="CC", layer=0, linetype_scale=1):
        self.anchor = anchor
        self.layer = layer,
        self.linetype_scale = linetype_scale

class Rectangle(Props):
    def __init__(self, x, y, width, height, anchor, layer, linetype_scale):
        super().__init__(anchor, layer, linetype_scale)
        self.x = x
        self.y = y
        self.width = width
        self.height = height

class Square(Props):
    def __init__(self, x, y, width, anchor, layer, linetype_scale):
        super().__init__(anchor, layer, linetype_scale)
        self.x = x
        self.y = y
        self.width = width

class Circle(Props):
    def __init__(self, x, y, diametar, anchor, layer, linetype_scale):
        super().__init__(anchor, layer, linetype_scale)
        self.x = x
        self.y = y
        self.diametar = diametar

What I want to be able to do is to call class without passing arguments for example:

rect = Rectangle(10, 10, 20, 50)

but if i need to change anything to be able to do this:

rect = Rectangle(10, 10, 20, 50, linetype_scale=5)

did you make a copy error? you Props class doesn't have an __init__, but instead has init — Nullman
– Nullman, Commented Nov 2, 2021 at 10:41
Sorry that was just copy error I fixed that. I my code is __init__ — Klak031
– Klak031, Commented Nov 2, 2021 at 10:43
You see how writing def __init__(self, anchor="CC", layer=0, linetype_scale=1): makes it possible not to need an explicit value for anchor, layer or linetype_scale when you create a Props directly? Did you try applying the same technique for the other __init__ methods? — Karl Knechtel
– Karl Knechtel, Commented Nov 2, 2021 at 10:48

Maurice Meyer · Accepted Answer · 2021-11-02 10:45:47Z

4

You could make use of **kwargs, which are passed to Props if given, otherwise the defaults from Props are used:

class Props():
    def __init__(self, anchor="CC", layer=0, linetype_scale=1):
        self.anchor = anchor
        self.layer = layer,
        self.linetype_scale = linetype_scale


class Rectangle(Props):
    def __init__(self, x, y, width, height, **kwargs):
        super().__init__(**kwargs)
        self.x = x
        self.y = y
        self.width = width
        self.height = height


rect1 = Rectangle(10, 10, 20, 50)
rect2 = Rectangle(10, 10, 20, 50, linetype_scale=5)

print(rect1.linetype_scale)
print(rect2.linetype_scale)

Out:

1
5

answered Nov 2, 2021 at 10:45

Maurice Meyer

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