HTTPException usage in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when HTTPException is raised in FastAPI?

Consider this FastAPI endpoint code:

from fastapi import FastAPI, HTTPException
app = FastAPI()

@app.get('/items/{item_id}')
async def read_item(item_id: int):
    if item_id < 1:
        raise HTTPException(status_code=400, detail='Invalid item ID')
    return {'item_id': item_id}

What will the client receive if they request /items/0?

FastAPI

from fastapi import FastAPI, HTTPException
app = FastAPI()

@app.get('/items/{item_id}')
async def read_item(item_id: int):
    if item_id < 1:
        raise HTTPException(status_code=400, detail='Invalid item ID')
    return {'item_id': item_id}

A A JSON response with status 400 and body {"detail": "Invalid item ID"}

B A server crash with a traceback error

C A JSON response with status 200 and body {"item_id": 0}

D A redirect to the root path '/'

💡 Hint

Think about what HTTPException does in FastAPI when raised inside a route.

Raising HTTPException in FastAPI immediately returns an HTTP response with the given status code and detail as JSON. It does not crash the server or redirect.

📝 Syntax

intermediate

Identify the correct way to raise HTTPException with a custom header

Which of the following code snippets correctly raises an HTTPException with status 403 and a custom header X-Error: Forbidden?

A raise HTTPException(status_code=403, detail='Forbidden', headers={'X-Error': 'Forbidden'})

B raise HTTPException(403, 'Forbidden', headers={'X-Error': 'Forbidden'})

C raise HTTPException(status=403, message='Forbidden', headers={'X-Error': 'Forbidden'})

D raise HTTPException(code=403, detail='Forbidden', header={'X-Error': 'Forbidden'})

💡 Hint

Check the exact parameter names in HTTPException constructor.

The HTTPException constructor expects named parameters: status_code, detail, and headers. Option A uses correct parameter names and syntax.

🔧 Debug

advanced

Why does this HTTPException raise a TypeError?

Given this code snippet:

from fastapi import HTTPException

raise HTTPException(status_code=404, detail=123)

What error will occur and why?

FastAPI

from fastapi import HTTPException

raise HTTPException(status_code=404, detail=123)

A SyntaxError due to missing parentheses

B No error, it raises HTTPException with detail 123

C ValueError because status_code 404 is invalid

D TypeError because detail must be a string or dict, not an integer

💡 Hint

Check the expected type for the detail parameter in HTTPException.

The detail parameter should be a string, dict, or list. Passing an integer causes a TypeError when FastAPI tries to serialize the response.

❓ state_output

advanced

What is the response status code after catching HTTPException?

Consider this FastAPI code:

from fastapi import FastAPI, HTTPException
app = FastAPI()

@app.get('/test')
async def test():
    try:
        raise HTTPException(status_code=401, detail='Unauthorized')
    except HTTPException as e:
        return {'caught': True, 'status': e.status_code}

What will the HTTP status code of the response be when calling /test?

FastAPI

from fastapi import FastAPI, HTTPException
app = FastAPI()

@app.get('/test')
async def test():
    try:
        raise HTTPException(status_code=401, detail='Unauthorized')
    except HTTPException as e:
        return {'caught': True, 'status': e.status_code}

A 500 Internal Server Error due to unhandled exception

B 401 Unauthorized with JSON body {'caught': True, 'status': 401}

C 200 OK with JSON body {'caught': True, 'status': 401}

D No response because the server crashes

💡 Hint

Think about what happens when you catch the exception and return a normal dict.

Catching HTTPException prevents it from propagating. Returning a dict sends a 200 OK response with that JSON body.

🧠 Conceptual

expert

Which statement about HTTPException in FastAPI is true?

Select the one correct statement about how HTTPException works in FastAPI.

A HTTPException can only be raised inside dependency functions, not route handlers.

B Raising HTTPException immediately returns an HTTP response with the given status and detail without executing further code in the route.

C HTTPException automatically logs the error to a file named 'http_errors.log'.

D Raising HTTPException changes the global server status code for all future requests.

💡 Hint

Think about the purpose of HTTPException in request handling.

Raising HTTPException stops the current route execution and sends the specified HTTP error response immediately. It does not log automatically or affect global server state.