Chain of Responsibility (Python)

Why: Chain of Responsibility lets you pass a request (or context) along a chain of handlers. Each handler decides whether to process it and pass to the next, or short-circuit. You avoid one big function with all steps and keep each step in its own class (Refactoring.Guru).

Hard constraints: Handlers share a single interface (e.g. handle(context)). Each handler holds a reference to the next; the client composes the chain. A handler either processes and passes, or passes without processing.

When to use

• Validation: Multi-rule validation (required → format → range) where you want to add or reorder rules without editing a single validator.
• Any sequential pipeline: Processing steps, transformation chains, or multi-step checks where order matters and each step can process and pass (or stop).
• You want to decouple the sender from concrete handlers and add or reorder steps without changing existing code (Single Responsibility; Open/Closed).

Structure