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Plugin Discovery, Registration, and Sandboxing

Concept Position

flowchart TD
  family["Python Programming"] --> program["Python Object-Oriented Programming"]
  program --> module["Module 09: Public APIs, Extension Seams, and Governance"]
  module --> concept["Plugin Discovery, Registration, and Sandboxing"]
  concept --> capstone["Capstone pressure point"]
flowchart TD
  problem["Start with the design or failure question"] --> example["Study the worked example and trade-offs"]
  example --> boundary["Name the boundary this page is trying to protect"]
  boundary --> proof["Carry that question into code review or the capstone"]

Read the first diagram as a placement map: this page is one concept inside its parent module, not a detached essay, and the capstone is the pressure test for whether the idea holds. Read the second diagram as the working rhythm for the page: name the problem, study the example, identify the boundary, then carry one review question forward.

Purpose

Support plugins only when the system can discover, validate, and constrain them with clear lifecycle and safety rules.

1. Plugins Add Governance Cost

Plugin support is not "more extensible for free." It adds questions about:

  • discovery
  • registration order
  • version compatibility
  • failure isolation
  • security and trust

If those questions are not worth answering, do not add plugins yet.

2. Registration Should Validate Capability and Metadata

A plugin loader should check:

  • required interface or protocol support
  • version compatibility
  • unique names or identifiers
  • declared configuration needs

Loose registration invites runtime surprises.

3. Discovery Mechanisms Need Intent

Possible approaches:

  • explicit configuration
  • package entry points
  • module scanning inside a trusted namespace

Choose the simplest mechanism that matches the deployment model.

4. Sandboxing Is Usually a Process Boundary Problem

In-process plugins share memory and failure modes with the host. If untrusted code is involved, real isolation usually requires a stronger boundary than a Python interface.

Practical Guidelines

  • Add plugin support only when you can justify its governance cost.
  • Validate plugin metadata and capability before registration.
  • Prefer explicit discovery over magical scanning when clarity matters.
  • Do not confuse in-process plugins with real sandboxing.

Exercises for Mastery

  1. Decide whether one customization need in your system truly requires plugins.
  2. Define the metadata a plugin should declare before registration.
  3. Document which plugins are trusted in-process and which would require stronger isolation.