Can you give an example of dependency usage in FastAPI?

In FastAPI, dependencies are used to inject reusable components, such as database connections, authentication, or common configurations.

Example: a function that returns the current user can be a dependency for different routes.

from fastapi import FastAPI, Depends, HTTPException

app = FastAPI()

def get_current_user(token: str):
    if token != "secret-token":
        raise HTTPException(status_code=401, detail="Invalid token")
    return "user123"

@app.get("/profile")
async def read_profile(current_user: str = Depends(get_current_user)):
    return {"user": current_user}

Here, Depends allows get_current_user to be called automatically and its result passed to the handler.