dependency_injection

id	modern/dependency_injection
name	Dependency Injection
aliases	DI constructor-injection inversion-of-control
guide_url
problem	Hand an object its collaborators instead of letting it construct them, so they can be swapped — above all in tests.
symptoms	can't test without the real database class news up its own client mock the clock swap implementation per environment
verdict	pythonic
caveats	In Python DI needs no framework: a keyword argument with a production default is the entire mechanism. Inject at the boundary that varies (clock, storage, transport) — injecting everything turns constructors into wiring diagrams.
stdlib_sightings	json.dumps cls= sorted key= unittest.mock

Dependency Injection

Hand an object its collaborators — clock, storage, transport — instead of letting it construct them, so tests can swap in fakes. Verdict: pythonic — a keyword argument with a production default is the whole mechanism.

Where	What
pattern/	The importable code: ReminderService, InvoiceSource, MailTransport, Clock
docs/	Fundamentals · Implementation guide · External examples
examples/invoice_reminders/	Mini-project: adapters + a real composition root over pattern/
tests/	Behavioral tests for the pattern and the mini-project

uv run python -m patterns.modern.dependency_injection.examples.invoice_reminders.main