Depends is dependency injection.But it isn't dependency inversion (or DIP) within SOLID.
Two patterns with similar names: one interface I kept, one I deleted, and the point where FastAPI's own mechanism stops being enough.
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Iryna Ostapchuk — backend Python dev. FastAPI web applications
I write about the things that didn't work the first time.
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The Protocol I wrote and then deleted
An interface with one implementation describes that implementation twice. The one I kept exists for a different reason entirely.
The refusal said the same thing. It did not take the same time!
Unknown address and wrong password returned an identical message — and very different response times, because short-circuiting skipped the hash.
The JWT claim that lost a fraction of a second and it kills all auth
A password change should end older sessions. It sometimes ended the new one too, because PyJWT truncates a datetime claim to whole seconds. And you can never claim your own JWT!
A circular import told me where I should start my app
Suddenly, my app crashed. It stopped importing. The first fix was to break the cycle — and then it was to notice that pagination had never belonged next to posts. How tragic it was...
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Updated 28 Jul 2026
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