Factory Design Pattern

Video Lecture

Description

The Factory Pattern is a creational pattern that defines an Interface for creating an object and defers instantiation until runtime.

Used when you don't know how many or what type of objects will be needed until or during runtime

The Factory Pattern in the context of a Chair Factory

Source Code

chair_factory.py

from abc import ABCMeta, abstractstaticmethod


class IChair(metaclass=ABCMeta):  # pylint: disable=too-few-public-methods
    """The Chair Interface"""

    @abstractstaticmethod
    def dimensions():
        """A static inteface method"""


class BigChair(IChair):  # pylint: disable=too-few-public-methods
    """The Big Chair Concrete Class which implements the IChair interface"""

    def __init__(self):
        self._height = 80
        self._width = 80
        self._depth = 80

    def dimensions(self):
        return {"width": self._width, "depth": self._depth, "height": self._height}


class MediumChair(IChair):  # pylint: disable=too-few-public-methods
    """The Medium Chair Concrete Class which implements the IChair interface"""

    def __init__(self):
        self._height = 60
        self._width = 60
        self._depth = 60

    def dimensions(self):
        return {"width": self._width, "depth": self._depth, "height": self._height}


class SmallChair(IChair):  # pylint: disable=too-few-public-methods
    """The Small Chair Concrete Class which implements the IChair interface"""

    def __init__(self):
        self._height = 40
        self._width = 40
        self._depth = 40

    def dimensions(self):
        return {"width": self._width, "depth": self._depth, "height": self._height}


class ChairFactory:  # pylint: disable=too-few-public-methods
    """Tha Factory Class"""

    @staticmethod
    def get_chair(chair):
        """A static method to get a table"""
        try:
            if chair == "BigChair":
                return BigChair()
            if chair == "MediumChair":
                return MediumChair()
            if chair == "SmallChair":
                return SmallChair()
            raise AssertionError("Chair Not Found")
        except AssertionError as _e:
            print(_e)
        return None


if __name__ == "__main__":
    CHAIR_FACTORY = ChairFactory().get_chair("SmallChair")
    print(CHAIR_FACTORY.dimensions())