The Factory Method Pattern and Its Implementation in Python | kabobconnection

The Factory Method Pattern and Its Implementation in Python

The factory creates the concrete implementation of the music service based on the specified key parameter. The new design of Factory Method allows the application to introduce new features by adding new classes, as opposed to changing existing ones. You can serialize other objects by implementing the Serializable interface on them. You can support new formats by implementing the Serializer interface in another class. The current implementation of .get_serializer() is the same you used in the original example. The method evaluates the value of format and decides the concrete implementation to create and return.

This way, we can add any number of add-ons to a specific coffee blend. // check if the instance is null, and if so, create the object. You know that this is not what happens because the Builder class keeps the initialized instance and returns it for subsequent calls, but this isn’t clear from just reading the code. In the following sections, you will solve this problems by generalizing the creation interface and implementing a general purpose Object Factory. You want your designs to be flexible, and as you will see, supporting additional formats without changing SerializerFactory is relatively easy.

Design patterns provide general solutions, documented in a format that doesn’t require specifics tied to a particular problem. Decorator is probably the most used Python pattern, because of in-built decorator support. For example, Decorator provides a convenient and explicit way to use some libraries and creates ever-richer opportunities for application design & management. The pattern also ensures a wide possibility for function composition and discovers new opportunities in functional programming. In nature, i.e. they may consist of more than one type of design pattern. Abstract Factory might consist of a set of Prototypes from which to clone.

  • We will use the factory method when a product does not know the exact subclass.
  • Turns a request into a stand-alone object that contains all information about the request.
  • The .get_serializer() method retrieves the registered creator and creates the desired object.
  • The Song class implements the Serializable interface by providing a .serialize method.
  • Lets you split a large class or a set of closely related classes into two separate hierarchies—abstraction and implementation—which can be developed independently of each other.
  • Here, we are creating the instance by using the new keyword.

Sometimes the nature of the object might change along with the change in classes, so in this case, the creational design patterns provide a flexible approach to handle this situation. Two main ideas that are being used in creational design patterns are encapsulating and hiding how these are created and combined. The factory method is used when the client-side object does not know which class to instantiate. It is a creational design pattern that defines or makes an abstract class for creating an object but allows to alter the type of created objects. This method can create instances of the appropriate classes by using the family hierarchy of classes.

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The local service is simpler, but it doesn’t match the initialization interface of the others. At the same time, other users want to integrate with Pandora. Pandora might use a completely different authorization process. It also requires a client key and secret, but it returns a consumer key and secret that should be used for other communications.

Creational Python Design Patterns

We will begin by looking at the code common to both versions, starting with the main() function. This may very well be the most famous Python design pattern. Think about its possible implementation in other languages such as Java and C#, and you’ll quickly realize the beauty of Python. That’s a dependency injection and it’s a powerful and easily mastered mechanism. Nevertheless, let’s see how we can implement a few, should we feel we might gain an advantage by using such patterns. This principle is deeply integrated in this design pattern.

It should do just one thing and have only one reason to change. For example, an application requires an object with a specific interface to perform its tasks. The concrete implementation of the interface is identified by some parameter. This is because the original design patterns were primarily …

Python Example code

➖ It’s hard to unit test the code as the majority of test frameworks use inheritance when creating mock objects. The pattern produces a decorator class to wrap the original one and add new functionality. I create the Facade class in case I have to work with complex libraries & APIs and/ or I need only the part of their functionality. Facade provides a simplified yet limited interface to decrease the complexity of an application. Complex subsystems with multiple moving parts could be “masked” by Facade.

Creational Python Design Patterns

Design patterns are quite often created for and used by OOP Languages, like Java, in which most of the examples from here on will be written. The .create() method requires that additional arguments are specified as keyword arguments. This allows the Builder objects to specify the parameters they need and ignore the rest in no particular order.

Design Patterns in Python

For example, you may need to create a main course and a dessert at an Italian and a French restaurant, but you won’t mix one cuisine with the other. Here, we’ve hardcoded the parameters for clarity, though typically you’d just instantiate the class and have it do its thing.

We derived one class from it in this case, but if we needed another Singleton for another purpose we could just derive the same metaclass instead of implementing essentially the same thing. Optional here is a data type which can contain either a class stated in [] or None. Having only one instance is usually a mechanism for controlling access to some shared resource. For example, two threads may work with the same file, so instead of both opening it separately, a Singleton can provide a unique access point to both of them.

The Factory pattern is a design pattern that allows you to use a function or method to handle the creation of an object. All of this means that our __call__ method will be called whenever a new object is created and it will provide a new instance if we haven’t already initialized one. If we have, it will just return the already initialized instance.

Creational Python Design Patterns

Python design patterns are a great way of harnessing its vast potential. We can not consider the Design Patterns as the finished design that python design patterns can be directly converted into code. They are only templates that describe how to solve a particular problem with great efficiency.

That being said, the Builder pattern doesn’t make much sense on small, simple classes as the added logic for building them just adds more complexity. Factories are used to encapsulate the information about classes we’re using, while instantiating them based on certain parameters we provide them with. Say you’re making software for an insurance company which offers insurance to people who’re employed full-time. Creational Design Patterns, as the name implies, deal with the creation of classes or objects.

1. Abstract Factory Pattern

Creational design patterns concern themselves with the instantiation of objects. At the time of creation, additional logic may be needed to decide what or how object types need to be created. The singleton design pattern is designed to solve two common problem.

While a Factory Method can produce only one type of object , an Abstract Factory can produce a family of different kinds of objects (multi-course and multi-cuisine meals). One generalized factory can consist of multiple specialized factories, each producing a different kind of object. In Java, the keyword synchronized is used on methods or objects to implement thread safety, so that only one thread will access a particular resource at one time. The class instantiation is put within a synchronized block so that the method can only be accessed by one client at a given time.

Creational Python Design Patterns

Don’t Repeat Yourself and never write code lines longer than 80 characters. And don’t forget to use design patterns where applicable; it’s one of the best ways to learn from others and gain from their wealth of experience free of charge. Provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created. The Model-View-Controller paradigm is touted as an example of a “pattern” which predates the concept of “design patterns” by several years. Pattern helps in the reuse of objects that are expensive to create by recycling objects which are no longer in use. It is most effective in situations where the rate and cost of instantiating a class is high.

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The DiagramFactory and its SvgDiagramFactory subclass, and the classes they make use of (Diagram, SvgDiagram, etc.), work perfectly well and exemplify the design pattern. For the SvgDiagram class, each instance holds a list of strings in self.diagram, each one of which is a piece of SVG text. This makes adding new components (e.g., of type SvgRectangle or SvgText) really easy.

Gang of Four: Structural Patterns¶

Creational patterns provides essential information regarding the Class instantiation or the object instantiation. Class Creational Pattern and the Object Creational pattern is the major categorization of the Creational Design Patterns. I’m Brandon Rhodes and this is my evolving guide to design patterns in thePython programming language.

Factory design patterns

If the implementation is easy to explain, it may be a good idea. A Singleton only allows one, and one object only to be instantiated from a class. Within this article, we will cover the Creational Patterns based upon the Python language.


Notice that SpotifyServiceBuilder keeps the service instance around and only creates a new one the first time the service is requested. This avoids going through the authorization process multiple times as specified in the requirements. This is referred to as the client component of the pattern. The interface defined is referred to as the product component.

We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes. We use this information to address the inquiry and respond to the question. Authors are vetted experts in their fields and write on topics in which they have demonstrated experience. All of our content is peer reviewed and validated by Toptal experts in the same field. Create one instance somewhere at the top-level of your application, perhaps in the config file.

It cars, bicycle, pizza, atm machines, whatever…even your sofa bed. Singleton PatternEnsures a class has only one object instantiated during the programs lifecycle. Donations to freeCodeCamp go toward our education initiatives, and help pay for servers, services, and staff.

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