Python & FastAPI

Python, Django, FastAPI, Flask, async Python

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Test yourself: Top 30 Python & FastAPI interview questions →Multiple choice, with the correct answer and why it is correct on every question. Free, no sign-in.

Interview questions in Python & FastAPI, page 7

advanced1 min read

Limits of BackgroundTasks vs Celery or ARQ

BackgroundTasks run in the same worker with no persistence, retries, or visibility, and die with the process; Celery or ARQ add durability, retries, scheduling, and separate workers.

advanced1 min read

Zero-downtime blue-green deploys on Kubernetes

Run blue and green deployments, switch a Service or ingress selector to the new color after readiness probes pass, drain old pods gracefully, and handle backward-compatible DB migrations.

intermediate1 min read

Secure refresh token flow for access renewal

Short-lived access token, longer-lived refresh token stored server-side, a refresh endpoint that validates and rotates the refresh token issuing a new pair.

intermediate1 min read

Testing a DB endpoint via dependency override

Use app.dependency_overrides to swap the real get_db for one yielding a test database session, run against a disposable SQLite or test Postgres, and assert through TestClient.

intermediate1 min read

Pydantic BaseModel vs dataclasses in FastAPI

BaseModel validates and coerces data at runtime, parses and serializes JSON, integrates with OpenAPI schema generation, and supports rich validators; dataclasses only store data with no validation.

intermediate1 min read

Mapping camelCase JSON to snake_case Pydantic fields

Set an alias_generator (to_camel) plus populate_by_name in model config, accept aliases on input, and serialize with by_alias=True so responses come out camelCase.

intermediate1 min read

Pydantic computed fields in response models

A @computed_field decorated property is excluded from input and validation but included in serialization and the OpenAPI schema, ideal for values like full_name derived from other fields.

intermediate1 min read

Streaming large file downloads efficiently

Use StreamingResponse with a generator that yields chunks (or FileResponse for an on-disk file), set media_type and a Content-Disposition header, so memory stays flat regardless of file size.

intermediate1 min read

Feature-based vs layer-based project structure

Layer-based groups by technical role and is simple early but scatters a feature across folders; feature-based groups by domain, improving cohesion and ownership at the cost of some duplication and…

intermediate2 min read

selectinload vs joinedload for eager loading

Use eager loading options to avoid lazy N+1; joinedload uses a single JOIN (good for many-to-one) but can fan out rows on collections; selectinload issues a second IN query (better for one-to-many).

intermediate2 min read

OAuth2 social login with your own JWT

A login endpoint redirects to the provider with a state param, a callback exchanges the code for the provider token, you fetch the user profile, upsert the local user, then mint your own JWT.

intermediate2 min read

Reading the full response body in middleware

Responses stream as multiple body messages and headers go first, so you cannot add a header after seeing the body; you must buffer all chunks, compute the hash, set the header, then resend.

intermediate2 min read

Choosing Uvicorn worker count in production

Workers exist to use multiple CPU cores past the GIL; a common starting point ties count to cores, then you tune by load testing, balancing CPU and memory (each worker is a full copy) against connection-pool…

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