Design Patterns are reusable solutions to commonly occurring problems in software design. They are not ready-made solutions, but rather templates that we can customize to suit the specific needs of our program.
Design Patterns can be classified as creational, structural or behavioral depending on their purpose. Creational patterns concern the process of object creation. Structural patterns deal with the composition of classes or objects. Behavioral patterns characterize the ways in which classes or objects interact and distribute responsibility.
| Creational | Structural | Behavioral |
|---|---|---|
| Builder | Adapter | Chain of Responsibility |
| Factory Method | Bridge | Command |
| Abstract Factory | Composite | Interpreter |
| Prototype | Decorator | Iterator |
| Singleton | Façade | Mediator |
| Flyweight | Memento | |
| Proxy | Observer | |
| State | ||
| Strategy | ||
| Template Method | ||
| Visitor |
The SOLID principles were first promoted by Robert C. Martin (also known as Uncle Bob) in his 2000 paper, while the acronym was introduced some time later by Michael Feathers. They are a set of principles that guide the design of Object-Oriented Programming, and they provide the fundamental ideas behind Design patterns. Their aim is to make code more understandable, flexible and maintainable.
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Single Responsibility Principle: A class should do one thing and therefore it should have only a single reason to change.
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Open/Closed Principle: Classes should be open for extension (adding new functionality) and closed to modification (changing the code of an existing class).
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Liskov Substitution Principle: Subclasses should be substitutable for their base classes.
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Interface Segregation Principle: Clients should not be forced to depend upon interfaces that they do not use.
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Dependency Inversion Principle: Classes should depend upon interfaces or abstract classes instead of concrete classes and functions.
In this miniseries workshop, we will explore how to use Design Patterns to help us write better code. For each pattern, we will present:
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A simple code example where we do not use any patterns, and there is some issue that needs to be solved.
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The same code but using the selected pattern to solve that issue.
The examples are in Python, however, the principles are applicable to all Object-Oriented Programming.
If you would like to dive deeper into this topic, you can try this Udemy course that explains Design Patterns one by one with Python examples and hands-on exercises. You can also refer to the classic Design Patterns: Elements of Reusable Object-Oriented Software book. This online catalog is also very handy when you are trying to apply the patterns in your daily work.