Design Patterns and Refactoring in Python

Level up from writing code that works to writing code that lasts. This hands-on Python course teaches design patterns and refactoring through realistic, multi-file projects set inside a fictional consultancy, Refactor & Co. Learn to diagnose code smells, apply the most useful Gang of Four patterns the Pythonic way, and refactor tangled legacy code into clean, maintainable systems. Cover creational, structural, and behavioral patterns alongside modern backend techniques like the Repository pattern, Dependency Injection, and Result types. Every pattern is taught with honest tradeoffs: when it earns its keep, when Python's language features replace it, and when reaching for it makes code worse. Perfect for intermediate Python developers ready to write production-quality code and make confident design decisions.

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Course Chapters

1

The Case for Better Code

Set the stage for the course by exploring why patterns and refactoring matter before learning any specific techniques. Meet the Refactor & Co consultancy, see the difference between code that works and code that's good, understand the real cost of technical debt, and learn how design patterns give developers a shared vocabulary for talking about software design.

4 lessons
2

Code Smells

Learn to recognize the warning signs that code needs refactoring before reaching for any pattern. Work through the most common code smells in real-world Python — long methods, god objects, primitive obsession, feature envy, shotgun surgery, and duplicated code. Train your eye to diagnose problems precisely so you can choose the right refactoring move later.

9 lessons
3

Refactoring Fundamentals

Master the mechanical refactoring moves you'll use throughout your career as a Python developer. Learn to extract methods, rename for clarity, replace magic numbers with named constants, swap long conditionals for polymorphism, and bundle related primitives into parameter objects. These foundational techniques set up everything that follows in the course.

8 lessons
4

Pythonic Foundations

Learn the Python-specific language features that change how classical design patterns apply. Master first-class functions, duck typing with typing.Protocol, dataclasses, and modules as natural singletons. This chapter prevents the common mistake of writing Java-style patterns in Python and prepares you to spot when language features already solve the problem.

7 lessons
5

Creational Patterns

Learn the Gang of Four patterns that solve the problem of creating objects: Simple Factory, Factory Method, Builder, and the Singleton (and why to avoid it). Understand when centralizing construction logic pays off and when a plain class constructor is the right call. Includes a decision guide and a hands-on refactoring exercise that transforms constructor hell into clean object creation.

10 lessons
6

Structural Patterns

Learn how to compose objects into larger, well-organized structures using the Adapter, Decorator, Facade, and Composite patterns. Adapt incompatible interfaces, wrap objects with additional behavior, hide subsystem complexity behind a simple API, and build recursive tree structures. Connects the classical Decorator pattern to Python's @ decorator syntax so you understand both versions of the idea.

11 lessons
7

Behavioral Patterns: Strategy, Template Method, State

Master the behavioral patterns that govern how objects choose and change their behavior at runtime. Learn Strategy for swapping algorithms, Template Method for fixed skeletons with customizable steps, and State for objects that transition between modes. Includes honest comparisons — Strategy vs Template Method, State vs Strategy — and a refactoring exercise that converts a tangled stateful order processor into clean state classes.

11 lessons
8

Behavioral Patterns: Observer, Command, Iterator

Learn the behavioral patterns that drive event-driven systems, undo/redo functionality, and Python's iteration protocol. Master Observer for decoupled event notification, Command for encapsulating actions as objects, and Iterator as it appears natively through Python generators. Connects these patterns to real systems students already use — Django signals, Celery task queues, and for-loops.

10 lessons
9

Modern Patterns for Real Backend Code

Move beyond the classical Gang of Four catalog to learn the patterns senior Python developers actually use in production backend code. Master the Repository pattern for separating domain logic from storage, Dependency Injection for testable services, and Result types for explicit error handling without exceptions. Build the skills needed to write maintainable, testable services in real Python applications.

10 lessons
10

Patterns in Combination

See how design patterns work together in realistic, multi-file systems — because real software is never a single pattern in isolation. Design a notification system using Strategy, Factory, and Observer. Build a plugin architecture, an undo/redo system, and a rules engine that each combine multiple patterns. Finishes with a tour of Django class-based views to reveal the patterns hiding in code you already use.

8 lessons
11

Judgment and Wrap-up

Develop the judgment to know when patterns help and when they hurt — the hardest and most important skill in software design. Study real examples of pattern overuse, learn a practical decision framework that starts with the smell rather than the solution, get a quick tour of the patterns we deliberately skipped, and finish with a graduation refactoring project where you choose your own approach. Leave Refactor & Co ready to take on your own clients.

7 lessons