Status code control in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What status code does this FastAPI endpoint return?

Consider this FastAPI endpoint code. What HTTP status code will the client receive when calling /items/42?

FastAPI

from fastapi import FastAPI
from fastapi.responses import JSONResponse

app = FastAPI()

@app.get('/items/{item_id}')
async def read_item(item_id: int):
    if item_id == 42:
        return JSONResponse(content={'item_id': item_id}, status_code=202)
    return {'item_id': item_id}

A 200

B 500

C 404

D 202

💡 Hint

Look at the status_code parameter in JSONResponse for item_id 42.

When item_id is 42, the endpoint returns a JSONResponse with status_code=202. Otherwise, it returns a default 200 response.

📝 Syntax

intermediate

Which option correctly sets a 201 status code for a POST endpoint?

You want to create a FastAPI POST endpoint that returns status code 201 when a new item is created. Which code snippet correctly sets this status code?

A

@app.post('/items')
async def create_item(item: dict):
    return Response(content=item, status_code=201)

B

@app.post('/items')
async def create_item(item: dict):
    return JSONResponse(content=item, status_code=201)

C

@app.post('/items', status_code=201)
async def create_item(item: dict):
    return item

D

@app.post('/items')
async def create_item(item: dict):
    return {'item': item, 'status': 201}

💡 Hint

Check how FastAPI allows setting status codes directly in the decorator.

Option C uses the status_code parameter in the decorator, which is the recommended way to set the response status code for simple returns.

🔧 Debug

advanced

Why does this FastAPI endpoint always return status 200 instead of 404?

Examine the code below. The intention is to return 404 if the item is not found. Why does it always return 200?

FastAPI

from fastapi import FastAPI, HTTPException

app = FastAPI()

items = {1: 'apple', 2: 'banana'}

@app.get('/items/{item_id}')
async def get_item(item_id: int):
    if item_id not in items:
        raise HTTPException(status_code=404, detail='Item not found')
    return {'item': items[item_id]}

A HTTPException must be raised, not returned, to trigger the error response.

B The status_code 404 is invalid and defaults to 200.

C The items dictionary is empty, so the condition never triggers.

D FastAPI does not support HTTPException for status control.

💡 Hint

Think about how exceptions work in Python and FastAPI.

Returning HTTPException just sends it as a normal response body with status 200. You must raise it to trigger the error status.

❓ state_output

advanced

What is the status code and response body when this FastAPI endpoint is called with /users/0?

Analyze the following FastAPI endpoint. What status code and JSON response will the client receive when requesting /users/0?

FastAPI

from fastapi import FastAPI, Response

app = FastAPI()

@app.get('/users/{user_id}')
async def get_user(user_id: int):
    if user_id == 0:
        return Response(content='User not found', status_code=404, media_type='text/plain')
    return {'user_id': user_id}

A Status code 404 with plain text body 'User not found'

B Status code 200 with JSON body {'user_id': 0}

C Status code 404 with JSON body {'detail': 'User not found'}

D Status code 500 with empty body

💡 Hint

Look at the Response object and its parameters.

The endpoint returns a Response with status 404 and plain text content 'User not found' when user_id is 0.

🧠 Conceptual

expert

Which statement about FastAPI status code control is true?

Select the correct statement about how FastAPI handles HTTP status codes in endpoint responses.

A Returning a dictionary from an endpoint always results in status code 500 unless a status_code is set explicitly.

B Setting status_code in the decorator changes the default response status code unless overridden by returning a Response with a different status_code.

C FastAPI automatically sets status code 201 for all POST requests regardless of decorator or return value.

D Raising HTTPException changes the response body but does not affect the HTTP status code sent to the client.

💡 Hint

Think about how decorator status_code and return values interact.

The status_code in the decorator sets the default status code. Returning a Response with a different status_code overrides it. Other options are incorrect.