CODEWITHSUNDEEP
pythonpython-3.xclassinheritancenested
EllipticalInitial
EllipticalInitial

Reputation: 1270

Python Parent Child Specific Class Structure

Suppose I have a 'composition' class and a 'layer' class. Suppose that an instance of the layer class cannot exist without an instance of the composition class, and an instance of the composition class can have multiple layer instances. Methods of the layer class need to be able to access the members of the composition class. This isn't exactly inheritance, because each layer instance should be 'contained' within a single instance of the composition class.

For example, if my composition class has three members "comp_width," "comp_height", and a list called "layers", each layer in the list should be able to call their own methods which have access to the "comp_width" and "comp_height" variables.

Is there some way to set up this particular structure of classes in Python? If so, can you give an example? I'm not sure if this can be done.

Upvotes: 1

Views: 246

Answers (1)

user10325516
user10325516

Reputation:

One approach is to create layers with already existing composition. This will allow you to pass composition object to every layer object during the creation.

class Layer:

    def __init__(self, composition, name):
        if not isinstance(composition, Composition):
            raise TypeError(
                'instance of the layer class cannot exist without an instance '
                'of the composition class')
        self.composition = composition
        self.name = name

    def __repr__(self):
        return self.name

    def get_composition_info(self):
        return (
            'composition [{}] with size [{} x {}] and layers {}'
            .format(
                self.composition.name,
                self.composition.height,
                self.composition.width,
                self.composition.layers))


class Composition:

    def __init__(self, name, height, width):
        self.layers = list()
        self.name = name
        self.height = height
        self.width = width

    def __repr__(self):
        return self.name

    def create_layer(self, name):
        layer = Layer(self, name)
        self.layers.append(layer)
        return layer


comp = Composition('my_composition_1', 10, 2)
l_1 = comp.create_layer('layer_1')
l_2 = comp.create_layer('layer_2')

print(comp)
print(comp.layers)
print(l_1)
print(l_1.get_composition_info())

Output of print()s:

my_composition_1
[layer_1, layer_2]
layer_1
composition [my_composition_1] with size [10 x 2] and layers [layer_1, layer_2]

Upvotes: 1

Related Questions