7.1. Composite

• EN: Composite

• PL: Kompozyt

• Type: object

7.1.1. Pattern

• Represent a hierarchy of objects

• Groups (and subgroups) objects in Keynote

• Files in a Folder; when you move folder you also move files

• allows you to represent individual entities and groups of entities in the same manner.

• is a structural design pattern that lets you compose objects into a tree.

• is great if you need the option of swapping hierarchical relationships around.

• makes it easier for you to add new kinds of components

• conform to the Single Responsibility Principle in the way that it separates the aggregation of objects from the features of the object.

7.1.2. Problem

from typing import Self
from dataclasses import dataclass, field


@dataclass
class Shape:
    name: str

    def render(self) -> None:
        print(f'Render {self.name}')

    def move(self) -> None:
        print(f'Move {self.name}')


@dataclass
class Group:
    objects: list[Shape | Self] = field(default_factory=list)

    def add(self, obj: Shape | Self) -> None:
        self.objects.append(obj)

    def render(self) -> None:
        for obj in self.objects:
            obj.render()

    def move(self) -> None:
        for obj in self.objects:
            obj.move()


if __name__ == '__main__':
    group1 = Group()
    group1.add(Shape('square'))
    group1.add(Shape('rectangle'))

    group2 = Group()
    group2.add(Shape('circle'))
    group2.add(Shape('ellipse'))

    everything = Group()
    everything.add(group1)
    everything.add(group2)

    everything.render()
    # Render square
    # Render rectangle
    # Render circle
    # Render ellipse

    everything.move()
    # Move square
    # Move rectangle
    # Move circle
    # Move ellipse

7.1.3. Solution

from abc import ABC, abstractmethod
from dataclasses import dataclass, field


class Component(ABC):
    @abstractmethod
    def render(self) -> None:
        pass

    @abstractmethod
    def move(self) -> None:
        pass


@dataclass
class Shape(Component):
    name: str

    def move(self) -> None:
        print(f'Move {self.name}')

    def render(self) -> None:
        print(f'Render {self.name}')


@dataclass
class Group(Component):
    components: list[Component] = field(default_factory=list)

    def add(self, component: Component) -> None:
        self.components.append(component)

    def render(self) -> None:
        for component in self.components:
            component.render()

    def move(self) -> None:
        for component in self.components:
            component.move()


if __name__ == '__main__':
    group1 = Group()
    group1.add(Shape('square'))
    group1.add(Shape('rectangle'))

    group2 = Group()
    group2.add(Shape('circle'))
    group2.add(Shape('ellipse'))

    everything = Group()
    everything.add(group1)
    everything.add(group2)

    everything.render()
    # Render square
    # Render rectangle
    # Render circle
    # Render ellipse

    everything.move()
    # Move square
    # Move rectangle
    # Move circle
    # Move ellipse

7.1.4. Assignments

from abc import ABC, abstractmethod
from dataclasses import dataclass, field


class Shape(ABC):
    @abstractmethod
    def print(self):
        pass


class Ellipse(Shape):
    def print(self):
        print('Ellipse')


class Circle(Shape):
    def print(self):
        print('Circle')


@dataclass
class Group(Shape):
    children: list = field(default_factory=list)

    def add(self, graphic):
        self.children.append(graphic)

    def print(self):
        for children in self.children:
            children.print()


if __name__ == '__main__':
    group1 = Group()
    group1.add(Ellipse())

    group2 = Group()
    group2.add(Circle())
    group2.add(group1)
    group2.print()