Lesson 07 · 10 min
Error handling
Your own exceptions, your own handlers, and one response format.
HTTPException is handy in routes, but the service layer shouldn't know about HTTP. It raises its own exceptions (BookNotFound), and @app.exception_handler turns them into a response with the right status. FastAPI raises validation errors as RequestValidationError and by default returns 422 with a detail field — you can set your own handler for those too.
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