Junior — Middle

What is the role of the Depends class in FastAPI and what tasks is it used for?

sobes.tech AI

Answer from AI

In FastAPI, the Depends class is used for dependency injection into request handlers. It allows you to define functions or classes that FastAPI will automatically call and pass the result into route parameters.

This is useful for:

Reusing code (e.g., authentication checks, database session retrieval)
Managing dependencies and their initialization
Improving code readability and testability

Example of usage:

from fastapi import Depends, FastAPI

def get_token_header(token: str):
    if token != "expected_token":
        raise HTTPException(status_code=400, detail="Invalid Token")

app = FastAPI()

@app.get("/items/")
async def read_items(token: str = Depends(get_token_header)):
    return [{"item": "Foo"}]

Here, Depends tells FastAPI to call the get_token_header function and pass its result into the token parameter.

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