Why error handling ensures reliability in FastAPI - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the FastAPI class.

FastAPI

from fastapi import [1]
app = [1]()

Drag options to blanks, or click blank then click option'

AHTTPException

BRequest

CResponse

DFastAPI

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Request or Response instead of FastAPI.

Trying to create app with a wrong class name.

FastAPI is the main class to create an app instance.

2fill in blank

medium

Complete the code to raise an HTTP 404 error when item not found.

FastAPI

from fastapi import HTTPException

@app.get('/items/{item_id}')
async def read_item(item_id: int):
    if item_id not in items:
        raise [1](status_code=404, detail='Item not found')
    return items[item_id]

Drag options to blanks, or click blank then click option'

AFastAPI

BHTTPException

CResponse

DRequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using Request or Response instead of HTTPException.

Not raising an exception at all.

HTTPException is used to raise HTTP errors in FastAPI.

3fill in blank

hard

Fix the error in the exception handler decorator.

FastAPI

@app.exception_handler([1])
async def http_exception_handler(request, exc):
    return JSONResponse(status_code=exc.status_code, content={'message': exc.detail})

Drag options to blanks, or click blank then click option'

AHTTPException

BRequest

CResponse

DFastAPI

Attempts:

3 left

💡 Hint

Common Mistakes

Using Request or Response in the decorator instead of HTTPException.

Not specifying any exception class.

The exception handler must specify the exception class it handles, here HTTPException.

4fill in blank

hard

Fill both blanks to return a JSON response with error details.

FastAPI

from fastapi.responses import [1]

@app.exception_handler(HTTPException)
async def http_exception_handler(request, exc):
    return [2](status_code=exc.status_code, content={'error': exc.detail})

Drag options to blanks, or click blank then click option'

AJSONResponse

BHTMLResponse

CPlainTextResponse

DRedirectResponse

Attempts:

3 left

💡 Hint

Common Mistakes

Importing or returning HTMLResponse or PlainTextResponse instead of JSONResponse.

Returning RedirectResponse which is for redirects.

JSONResponse is used to send JSON formatted responses in FastAPI.

5fill in blank

hard

Fill all three blanks to create a reliable endpoint with error handling.

FastAPI

from fastapi import FastAPI, HTTPException
from fastapi.responses import [1]

app = FastAPI()

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

@app.get('/items/{item_id}')
async def read_item(item_id: int):
    if item_id not in items:
        raise [2](status_code=404, detail='Item not found')
    return [3](content={'item': items[item_id]})

Drag options to blanks, or click blank then click option'

AJSONResponse

BHTTPException

CResponse

DRequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using Request instead of HTTPException for errors.

Returning HTTPException instead of a response.

Not importing JSONResponse.

We import JSONResponse to send JSON data, raise HTTPException for errors, and use JSONResponse to return data.

Practice

1. Why is error handling important in a FastAPI application?

easy

A. It helps keep the app stable and provides clear feedback to users.

B. It makes the app run faster by skipping checks.

C. It automatically fixes bugs without developer input.

D. It hides all errors so users never see any messages.

Solution

1. Step 1: Understand the role of error handling

   Error handling catches problems and prevents crashes, keeping the app stable.

2. Step 2: Recognize user feedback importance

   Good error handling sends clear messages so users know what went wrong.

3. Final Answer:

   It helps keep the app stable and provides clear feedback to users. -> Option A

4. Quick Check:

   Error handling = stability + clear feedback [OK]

Hint: Error handling = stability + clear user messages [OK]

Common Mistakes:

• Thinking error handling speeds up the app
• Believing errors fix themselves automatically
• Assuming hiding errors improves reliability

2. Which of the following is the correct way to raise an HTTP error in FastAPI?

easy

A. raise HTTPException(status_code=404, detail="Item not found")

B. throw HTTPError(404, "Item not found")

C. return Error(404, "Item not found")

D. error(404, "Item not found")

Solution

1. Step 1: Recall FastAPI error syntax

   FastAPI uses raise HTTPException(status_code=..., detail=...) to send errors.

2. Step 2: Identify correct syntax

   raise HTTPException(status_code=404, detail="Item not found") matches the correct syntax; others use invalid or non-existent functions.

3. Final Answer:

   raise HTTPException(status_code=404, detail="Item not found") -> Option A

4. Quick Check:

   Use raise HTTPException(...) for errors [OK]

Hint: Use raise HTTPException with status_code and detail [OK]

Common Mistakes:

• Using throw instead of raise
• Returning error instead of raising
• Calling non-existent error functions

3. What will be the HTTP response status code if this FastAPI endpoint raises HTTPException(status_code=400, detail="Bad request")?

medium

A. 500

B. 200

C. 404

D. 400

Solution

1. Step 1: Understand HTTPException usage

   Raising HTTPException with status_code=400 sets the response status to 400.

2. Step 2: Match status code to response

   The response will have status 400, indicating a client error (bad request).

3. Final Answer:

   400 -> Option D

4. Quick Check:

   HTTPException status_code = response status [OK]

Hint: Raised HTTPException status_code = HTTP response code [OK]

Common Mistakes:

• Assuming default 200 status on error
• Confusing 400 with 404 or 500
• Ignoring the status_code parameter

4. Identify the error in this FastAPI code snippet for error handling:

from fastapi import FastAPI, HTTPException
app = FastAPI()

@app.get("/items/{item_id}")
async def read_item(item_id: int):
    if item_id < 0:
        return HTTPException(status_code=400, detail="Invalid ID")
    return {"item_id": item_id}

medium

A. Function should not be async

B. Missing import for HTTPException

C. Should use raise instead of return for HTTPException

D. Path parameter should be a string, not int

Solution

1. Step 1: Check how HTTPException is used

   HTTPException must be raised, not returned, to send an error response.

2. Step 2: Identify the mistake in code

   The code returns HTTPException instead of raising it, so error handling won't work properly.

3. Final Answer:

   Should use raise instead of return for HTTPException -> Option C

4. Quick Check:

   Raise HTTPException, don't return it [OK]

Hint: Use raise, not return, for HTTPException [OK]

Common Mistakes:

• Returning HTTPException instead of raising
• Forgetting to import HTTPException
• Wrong parameter types for path

5. You want to ensure your FastAPI app returns a 404 error with a custom message when an item is not found in the database. Which approach best ensures reliability and user clarity?

hard

A. Return {"error": "Item not found"} with status code 200.

B. Raise HTTPException(status_code=404, detail="Item not found") inside the endpoint when the item is missing.

C. Print an error message to the console and return an empty response.

D. Ignore missing items and return an empty dictionary.

Solution

1. Step 1: Understand proper error signaling

   Raising HTTPException with 404 status clearly signals the error to clients.

2. Step 2: Compare alternatives for reliability

   Returning 200 with error message or ignoring errors confuses clients and reduces reliability.

3. Final Answer:

   Raise HTTPException(status_code=404, detail="Item not found") inside the endpoint when the item is missing. -> Option B

4. Quick Check:

   Raise HTTPException for clear, reliable error responses [OK]

Hint: Raise HTTPException with 404 for missing items [OK]

Common Mistakes:

• Returning error info with 200 status
• Ignoring errors instead of signaling
• Only logging errors without response