[Design Pattern] Factory Pattern

• is responsible soely for the wholesale creation of objects
  
  • It's like outsourcing the creation of objects involving several steps
• Motivation
  • 1. When object creation logic becomes too convoluted
    • When initialization procedure becomes too complex, wants to move this part of code somewhere
  • 2. Initializer is not descriptive
    • (in python) name is always __init__
    • cannot overload with same sets of arguments with different names
    • can potentially turn into "optional parameter hell"
• Variations of Factory Design Pattern
  • 1. A separate method (Factory Method)
    • separate methods are static methods
  • 2. That may exist in a separate class (Factory)
    • Example
      • 1. If there is a class called Food, then there would be a FoodFactory class
  • 3. Can create hierarchy of factories with abstract factory

Example

from enum import Enum
from math import *


class CoordinateSystem(Enum):
    CARTESIAN = 1
    POLAR = 2


class Point:
    def __str__(self):
        return f'x: {self.x}, y: {self.y}'

    def __init__(self, a, b):
        self.x = a
        self.y = b

# take out factory methods to a separate class
class PointFactory:
    @staticmethod
    def new_cartesian_point(x, y):
        return Point(x, y)

    @staticmethod
    def new_polar_point(rho, theta):
        return Point(rho * sin(theta), rho * cos(theta))


if __name__ == '__main__':
    p1 = Point(2, 3, CoordinateSystem.CARTESIAN)
    p2 = PointFactory.new_cartesian_point(1, 2)
    # or you can expose factory through the type
    p3 = Point.Factory.new_cartesian_point(5, 6)
    p4 = Point.factory.new_cartesian_point(7, 8)
    print(p1, p2, p3, p4)

References

• Design Patterns in Python, Dmitri Nesteruk:  https://www.udemy.com/course/design-patterns-python/