Python Design for CLI Scripts

Design patterns and principles for writing maintainable Python CLI tools and utilities. Based on A Philosophy of Software Design (Ousterhout), adapted for scripting contexts.

When to Activate

• Writing or modifying Python files
• Planning module decomposition
• Code review of Python changes
• Refactoring scripts that feel "messy"
• Adding a new subcommand or utility function

Core Thesis

The central challenge is managing complexity, not adding features.

Complexity is anything that makes code hard to understand or modify. It has three symptoms: