Software Design in Python - This Design Pattern Scares Me To Death

👉 Get real-time, search result data from Google, Youtube and more with SerpApi: https://serpapi.link/arjan-codes-jan-2025. Business rules have a nasty habit of spreading across your codebase: copied into APIs, reports, scripts, and slowly drifting out of sync. In this video, I start with a very real, very messy example of duplicated if-statements and show how it escalates into bugs and confusion. Then I refactor it step by step using the Specification Pattern, in a practical, Pythonic style that lets you compose rules, test them in isolation, and even turn your logic into data that can live in config files. 🔥 GitHub Repository: https://git.arjan.codes/2026/spec. 🎓 ArjanCodes Courses: https://www.arjancodes.com/courses. 💬 Join my Discord server: https://discord.arjan.codes. ⌨️ Keyboard I’m using: https://amzn.to/49YM97v. 🔖 Chapters: 0:00 Intro 0:49 What is the Specification Pattern 3:47 The Goal: Reusable, Composable Rules 4:21 Step 1: The Simplest Possible Predicate 13:56 Step 2: Make Defining Predicates Pleasant 16:48 Step 3: Generalize With Generics and Rule Factories 20:00 Step 4: A Single @Rule Decorator for All Rules 24:54 Step 5: Composing Rules in the User Domain 25:36 Step 6: Loading Rules From Config (Real Specification Power) 28:30 Final Thoughts #arjancodes #softwaredesign #python