Composition and Design Flexibility
Explore how to design flexible Python programs by using composition to build modular objects, delegating responsibilities to specialized classes, and applying dependency injection to enhance reuse and adaptability. Understand the benefits of breaking complex systems into manageable parts for cleaner, extensible code.
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As systems grow beyond single classes, developers sometimes create “God objects,” which are large classes that attempt to handle too many responsibilities. For example, a Vehicle class should not implement logic for fuel injection, radio tuning, or tire pressure measurement. Combining these responsibilities would make the code harder to maintain and understand.
Instead, developers often design systems the way engineers design machines. Systems are built from small, specialized components such as an engine, a dashboard, and a transmission, which are then assembled into a complete system. In software design, this approach is known as composition. Composition treats objects as modular components and delegates responsibilities to specialized classes, which keeps the codebase easier to maintain and extend.
The “has-a” relationship
Composition is the design principle where one class contains instances of other classes as attributes. We often call this a “has-a” relationship. A Vehicle has an Engine. A Dashboard has a ...