* Add dependencies with `yield`, a.k.a. exit steps, context managers, cleanup, teardown, ...

* This allows adding extra code after a dependency is done. It can be used, for example, to close database connections.

* Dependencies with `yield` can be normal or `async`, **FastAPI** will run normal dependencies in a threadpool.

* They can be combined with normal dependencies.

* It's possible to have arbitrary trees/levels of dependencies with `yield` and exit steps are handled in the correct order automatically.

* It works by default in Python 3.7 or above. For Python 3.6, it requires the extra backport dependencies:

* `async-exit-stack`

* `async-generator`

* New docs at [Dependencies with `yield`](https://fastapi.tiangolo.com/tutorial/dependencies/dependencies-with-yield/).

* Updated database docs [SQL (Relational) Databases: Main **FastAPI** app](https://fastapi.tiangolo.com/tutorial/sql-databases/#main-fastapi-app).

* PR [#595](https://github.com/tiangolo/fastapi/pull/595).