DRY Principle

DRY Principle#

The DRY principle is a core software development concept that states: “Every piece of knowledge or logic must have a single, unambiguous representation within a system.”.

👉 New to App-Generator? Sign IN with GitHub or Generate Web Apps in no time (free service).

Key aspects of DRY#

  • Core concept: Knowledge should exist in one place and be referenced elsewhere rather than duplicated

  • Purpose: Reduces redundancy and simplifies maintenance

  • Implementation: Uses abstraction, inheritance, and composition to reuse code

  • Benefits: Easier maintenance, fewer bugs, smaller codebase, and improved consistency

DRY in practice#

When applied to programming, DRY encourages:

  • Creating reusable functions/methods instead of copying code blocks

  • Using inheritance to share behavior between similar classes

  • Applying templates or partials for repeated UI elements

  • Centralizing configuration values rather than hardcoding them multiple places

  • Using constants and enums for values used throughout the codebase

Django’s DRY approach#

Django exemplifies DRY through:

  • Models that define data structure once, then generate database schemas and form validation

  • Template inheritance that allows common elements (headers, footers) to be defined once

  • Class-based views that encapsulate common patterns

  • URL routing that centralizes path definitions

  • Middleware that handles cross-cutting concerns in one place

The opposite of DRY is WET (“Write Everything Twice” or “We Enjoy Typing”), which leads to maintenance challenges and inconsistencies when changes are needed.