11.4. Abstract Factory

• EN: Abstract Factory

• PL: Fabryka Abstrakcyjna

• Type: object

The Abstract Factory pattern differs from the Factory Pattern in that it returns Factories, rather than objects of concrete class.

11.4.1. Pattern

• Provide an interface for creating families of related objects

• Factory Method is a method

• Abstract Factory is an abstraction (interface)

• Used for theme support (which generates buttons, inputs etc)

11.4.2. Problem

• Violates Open/Close Principle

• Hard to add a new theme

• Easy to accidentally use Material widget inside of Flat theme block

from enum import Enum


#%% Interfaces
class Widget:
    def render(self) -> None:
        raise NotImplementedError

class Button(Widget):
    pass

class Textbox(Widget):
    pass


#%% Material Theme
class MaterialButton(Button):
    def render(self) -> None:
        print('Material Button')

class MaterialTextbox(Textbox):
    def render(self) -> None:
        print('Material Textbox')


#%% Flat Theme
class FlatButton(Button):
    def render(self) -> None:
        print('Flat Button')

class FlatTextbox(Textbox):
    def render(self) -> None:
        print('Flat Textbox')


#%% Main
class Theme(Enum):
    MATERIAL = 1
    FLAT = 2


class ContactForm:
    def render(self, theme: Theme) -> None:
        if self.theme == Theme.MATERIAL:
            MaterialTextbox().render()
            MaterialButton().render()
        elif self.theme == Theme.FLAT:
            FlatTextbox().render()
            FlatButton().render()

11.4.3. Solution

#%% Interfaces
class Widget:
    def render(self) -> None:
        raise NotImplementedError

class Button(Widget):
    pass

class Textbox(Widget):
    pass

class WidgetFactory:
    def create_button(self) -> Button:
        raise NotImplementedError

    def create_textbox(self) -> Textbox:
        raise NotImplementedError


#%% Material Theme
class MaterialButton(Button):
    def render(self) -> None:
        print('Material Button')

class MaterialTextbox(Textbox):
    def render(self) -> None:
        print('Material Textbox')

class MaterialWidgetFactory(WidgetFactory):
    def create_button(self) -> Button:
        return MaterialButton()

    def create_textbox(self) -> Textbox:
        return MaterialTextbox()


#%% Ant Theme
class AntButton(Button):
    def render(self) -> None:
        print('Ant Button')

class AntTextbox(Textbox):
    def render(self) -> None:
        print('Ant Textbox')

class AntWidgetFactory(WidgetFactory):
    def create_button(self) -> Button:
        return AntButton()

    def create_textbox(self) -> Textbox:
        return AntTextbox()


#%% Main
class ContactForm:
    def render(self, factory: WidgetFactory) -> None:
        factory.create_textbox().render()
        factory.create_button().render()


if __name__ == '__main__':
    theme = MaterialWidgetFactory()
    ContactForm().render(theme)

11.4.4. Assignments