How do dependencies with `yield` manage resource lifetime in FastAPI?

Explains acquisition and cleanup around `yield`, including request and function scopes, streaming, and exception-safe ownership.

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A dependency with yield acquires a resource before the yield, provides the yielded value to downstream dependencies or the handler, and runs the code after yield as cleanup. A try/finally or context manager makes cleanup run when processing succeeds or fails. In current FastAPI, request scope is the default and cleanup runs after the response is sent; scope="function" cleans up after the handler finishes but before the response is sent. The chosen scope must keep the resource alive for every consumer that still needs it.

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Current FastAPI resource-lifetime knowledge and the judgment to align cleanup with actual resource use.

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Overview
A yield dependency is a resource-owner boundary, so cleanup timing must match the response path.
A dependency with yield acquires a resource before the yield, provides the yielded value to downstream dependencies or the handler, and runs the code after yield as cleanup. A try/finally or context manager makes cleanup run when processing succeeds or fails. In current FastAPI, request scope is the default and cleanup runs after the response is sent; scope="function" cleans up after the handler finishes but before the response is sent. The chosen scope must keep the resource alive for every consumer that still needs it.

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Assuming cleanup always runs immediately after the handler returns.
Using a function-scoped resource from a later stream.
Passing a yielded database session into background work.
Catching and silently swallowing downstream exceptions during cleanup.

How do dependencies with `yield` manage resource lifetime in FastAPI?

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