mediator

id	behavioral/mediator
name	Mediator
aliases	coordinator hub
guide_url
problem	Stop a web of objects from referencing each other by routing their interactions through one coordinator.
symptoms	widgets updating each other N-squared object references form fields with interdependent rules components need decoupling
verdict	use-with-care
caveats	The mediator earns its keep by deleting pairwise references; if it grows into a god object that knows everything, you traded a web for a blob. For pipeline-shaped decoupling, a queue between producers and consumers is the simpler mediator.
stdlib_sightings	queue.Queue asyncio.Queue

Mediator

Route component interactions through one coordinator that owns every rule. Verdict: use with care — excellent for genuinely tangled rules; watch for god-object drift.

Where	What
pattern/	The importable code: Field (dumb value holder) + Form (the mediator base owning recheck)
docs/	Fundamentals · Implementation guide · External examples
examples/checkout_form/	Mini-project: cascading checkout rules built on pattern/
tests/	Behavioral tests for the pattern and the mini-project

uv run python -m patterns.behavioral.mediator.examples.checkout_form.main