[Solved] What is the error in the following FastAPI code using sub-dependencies?... What is the error in the following FastAPI code using sub-dependencies? | FastAPI

FastAPI - Dependency Injection

What is the error in the following FastAPI code using sub-dependencies?

from fastapi import FastAPI, Depends

app = FastAPI()

def sub_dep():
    return "data"

def main_dep(data: str = Depends(sub_dep)):
    return data

@app.get("/test")
async def test_endpoint(info: str = Depends(main_dep())):
    return {"info": info}

ACalling main_dep() inside Depends instead of passing the function

BMissing return statement in sub_dep

CIncorrect route path syntax

DUsing async def for endpoint without await

Step-by-Step Solution

Solution:

Step 1: Identify how Depends should be used
Depends expects a function reference, not a function call. Calling main_dep() executes it immediately, which is wrong.
Step 2: Check the code for this mistake
The code uses Depends(main_dep()), which calls the function instead of passing it. It should be Depends(main_dep).
Final Answer:
Calling main_dep() inside Depends instead of passing the function -> Option A
Quick Check:
Depends needs function, not function call [OK]

Quick Trick: Pass function to Depends, don't call it [OK]

Common Mistakes:

MISTAKES

Calling dependency functions inside Depends()
Confusing async usage with dependency errors
Ignoring Depends syntax rules

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More FastAPI Quizzes

What is the error in the following FastAPI code using sub-dependencies?

Step 1: Identify how Depends should be used

Step 2: Check the code for this mistake

Final Answer:

Quick Check:

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