Question 1

What is Pydantic used for in FastAPI?

Accepted Answer

Pydantic defines the shape of data using Python type hints. FastAPI uses these models to validate incoming request bodies and to shape outgoing responses. If a request is missing a field or has the wrong type, FastAPI returns a clear 422 error before your code runs. Adding response_model to a route also filters the output, so fields such as password hashes are never sent to the client.

Question 2

What does Depends do in FastAPI?

Accepted Answer

Depends tells FastAPI to call a function, called a dependency, and pass its result into a route. It is FastAPI's way of injecting shared logic. Typical examples are a database session or the current logged-in user. The dependency runs for each request, and its result is available to the route. This keeps routes short and avoids repeating the same setup code.