Plugins case study: Pluggy

Recently I came upon Pluggy, a Python library for developing plugin systems. It was originally developed as part of the pytest project - known for its rich plugin ecosystem - and later extracted into a standalone library. You're supposed to reach out for Pluggy if you want to add a plugin system to your tool or library and want to use something proven rather than rolling your own. In this post I will share some notes on how Pluggy works, and will then review how it aligns with the fundamental concepts of plugin infrastructures. Using Pluggy Pluggy is built around the concept of hooks: functions that host applications or tools (from here on, just "hosts") expose and plugins implement. A host exposes hooks by using a decorator returned from pluggy.HookspecMarker and a plugin implements this hook using a decorator returned from pluggy.HookimplMarker. Pluggy's documentation explains this fairly well; in this post, I'll show how to implement the htmlize tool with some plugins, introduced…