Factory methods

Intermediate Object-Oriented Programming in Python

Jake Roach

Data Engineer

Conditional logic in a method

class Student:
    # Conditional logic with similar behavior for all conditions
    def explore_topic(self, resource_type, topic):
        if resource_type == "Textbook":
            print(f"Referencing {topic} using a textbook")
            self.reference_textbook(topic)

        elif resource_type == "Blog":
            print(f"Make sure to validate information provided in blogs!")
            self.reference_blog(topic)

        elif resource_type == "Video":
            self.reference_video(topic)

Factory methods

Design pattern that uses factory methods to create objects that are used in another method

Return objects that implement an interface
Reduce complexity in a method
Reusable, modular
_ to denote a factory method

First, let's take a look at products and concrete products!

...

  def _get_resource(self, resource_type):  
    if resource_type == "Textbook":
      # Textbook, Blog and Video are
      # all resources
      return Textbook()  

    elif resource_type == "Blog":
      return Blog()  

    elif resource_type == "Video":
      return Video()

Creating a Resource interface

class Resource(ABC):
    @abstractmethod
    def reference(self, topic):
        pass

class Textbook(Resource):
    def __init__(self):
        self.index = {"Object-oriented Programming": ["Inheritance", ...]}

    def reference(self, topic):
        print(f"Referencing {topic} using a textbook")
        return self.index.get(topic)

# Something similar for Blog, Video

Reworking explore_topic()

class Student:

    def explore_topic(self, resource_type, topic):
        if resource_type == "Textbook":
            texbook = Textbook()  # Creating an instance of class implementing Resource
            texbook.reference(topic)  # Call the reference() method

        elif resource_type == "Blog":
            blog = Blog()
            blog.reference(topic)

        elif resource_type == "Video":
            video = Video()
            video.reference(topic)

Creating a factory method

class Student:
    # Factory method to return Resource
    def _get_resource(self, resource_type):
        if resource_type == "Textbook":
            return Textbook()  
        elif resource_type == "Blog":
            return Blog()  
        elif resource_type == "Video":
            return Video()

    def explore_topic(self, resource_type, topic):
        resource = self._get_resource(resource_type)  # Retrieve the resource
        return resource.reference(topic)

Using factory methods

# Create a Student object, then have it reference a textbook
lester = Student()
lester.explore_topic("Textbook", "Object-oriented Programming")

# Each to switch to another resource
lester.explore_topic("Video", "Object-oriented Programming")

Referencing Object-oriented Programming using a textbook
["Inheritance", "Constructors", "Class-level methods"]

Video are helpful for visual or audatory learners
["Classes", "Methods", "Attributes", "self"]

Let's practice!

Intermediate Object-Oriented Programming in Python