examples.md

Registry — where it lives outside this repo

Cited, real implementations to study (or point an agent at) when designing or reviewing registry-shaped code.

Python standard library

• codecs.register / codecs.lookup. The encodings machinery is a full plugin registry: every "text".encode(name) is a lookup, and registered search functions can serve entirely new names. docs.python.org/3/library/codecs.html
• functools.singledispatch. A registry keyed by type instead of name, with the same decorator registration surface and MRO-aware lookup. docs.python.org/3/library/functools.html#functools.singledispatch
• atexit.register. A registry whose "dispatch" is the interpreter shutting down — registration as decorator, in the stdlib since forever. docs.python.org/3/library/atexit.html

Major ecosystems

• Flask route decorators. @app.route("/users") fills the URL map — a registry populated at import time, which is why a views module that never gets imported serves 404s (the caveat, in production form). flask.palletsprojects.com
• Django admin.site.register. The explicit-call flavor: the admin is a registry of model → options, filled in each app's admin.py — a module Django deliberately auto-imports, solving the import-time problem by convention. docs.djangoproject.com/en/stable/ref/contrib/admin/
• setuptools entry points. Registration moved out of code into package metadata, so plugins in other distributions are discoverable without any import — the industrial-strength answer to "a plugin nobody imports". packaging.python.org/en/latest/specifications/entry-points/

What to notice across all of them

Each one has an explicit answer to the two policy questions: unknown names (LookupError from codecs, 404 from Flask) and registration time (import side effects, auto-imported conventions, or metadata). When reviewing registry code, find both answers; if either is implicit, that's the bug waiting.