composite.py

"""
Composite
- A mechanism for treating individual (scalar) objects and composition of
  objects in a uniform matter

Motivation
- Objects use others' properties/members through inheritance and composition
- Composition lets us make compound objects
  - E.g., a mathematical expression composed of simple expressions; or
  - A grouping of shapes that consists of several shapes
- Composite design pattern is used to treat both single (scalar) and composite
  objects uniformly
  - I.e., Foo and Sequence (yielding Foo's) have common APIs
"""


class GraphicObject:
    def __init__(self, color=None):
        self.color = color
        self.children = []
        self._name = 'Group'

    @property
    def name(self):
        return self._name

    def _print(self, items, depth):
        items.append('*' * depth)
        if self.color:
            items.append(self.color)
        items.append(f'{self.name}\n')
        for child in self.children:
            child._print(items, depth + 1)

    def __str__(self):
        items = []
        self._print(items, 0)
        return ''.join(items)


class Circle(GraphicObject):
    @property
    def name(self):
        return 'Circle'


class Square(GraphicObject):
    @property
    def name(self):
        return 'Square'

DRAWING = GraphicObject()
DRAWING._name = 'My Drawing'
DRAWING.children.append(Square('Red'))
DRAWING.children.append(Circle('Yellow'))

GROUP = GraphicObject()
GROUP.children.append(Circle('Blue'))
GROUP.children.append(Square('Blue'))
DRAWING.children.append(GROUP)

print(DRAWING)