Custom response classes in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the base class for custom responses in FastAPI.

FastAPI

from fastapi.responses import [1]

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

AJSONResponse

BHTMLResponse

CResponse

DRedirectResponse

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a specific response class like JSONResponse instead of the base Response class.

The Response class is the base class for creating custom response classes in FastAPI.

2fill in blank

medium

Complete the code to create a custom response class named MyResponse inheriting from the base response class.

FastAPI

class MyResponse([1]):
    def __init__(self, content: str):
        super().__init__(content=content, media_type="text/custom")

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

AResponse

BJSONResponse

CHTMLResponse

DPlainTextResponse

Attempts:

3 left

💡 Hint

Common Mistakes

Inheriting from a specific response class instead of the base Response class.

Custom response classes should inherit from Response to define their own behavior.

3fill in blank

hard

Fix the error in the custom response class by completing the method that returns the response body as bytes.

FastAPI

class MyResponse(Response):
    def __init__(self, content: str):
        super().__init__(content=content, media_type="text/custom")

    def [1](self) -> bytes:
        return self.content.encode("utf-8")

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

Arender

Bget_body

Cto_bytes

Dcontent_bytes

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that FastAPI does not recognize for rendering response content.

The render method is used in FastAPI custom responses to convert content to bytes.

4fill in blank

hard

Fill both blanks to create a FastAPI route that returns the custom response with content 'Hello'.

FastAPI

from fastapi import FastAPI

app = [2]()

@app.get("/custom")
async def custom_route():
    return [1]("Hello")  # Use custom response class

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

AMyResponse

BFastAPI

CResponse

DJSONResponse

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the base Response class instead of the custom one.

Reassigning app incorrectly.

The route should return an instance of the custom response class MyResponse. The app is created by calling FastAPI().

5fill in blank

hard

Fill all three blanks to define a custom response class that sets a custom header and returns content as bytes.

FastAPI

from fastapi.responses import Response

class CustomHeaderResponse([1]):
    def __init__(self, content: str):
        headers = {"X-Custom-Header": [2]
        super().__init__(content=content, media_type="text/custom", headers=headers)

    def [3](self) -> bytes:
        return self.content.encode("utf-8")

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

AResponse

B"MyValue"

Crender

DJSONResponse

Attempts:

3 left

💡 Hint

Common Mistakes

Not quoting the header value string.

Using the wrong method name instead of render.

The custom response class inherits from Response, sets a header string value, and implements the render method to return bytes.

Practice

1. What is the main purpose of using Custom response classes in FastAPI?

easy

A. To handle user authentication

B. To create database models automatically

C. To control how FastAPI sends data back to the client

D. To manage background tasks

Solution

1. Step 1: Understand the role of response classes

   Response classes in FastAPI define how data is formatted and sent back to the client, such as JSON, HTML, or plain text.

2. Step 2: Identify the correct purpose

   Custom response classes let you control the exact format and headers of the response, improving clarity and compatibility.

3. Final Answer:

   To control how FastAPI sends data back to the client -> Option C

4. Quick Check:

   Custom response classes = control response format [OK]

Hint: Response classes define output format in FastAPI [OK]

Common Mistakes:

• Confusing response classes with database models
• Thinking they handle authentication
• Assuming they manage background tasks

2. Which of the following is the correct way to use a custom response class to return plain text in FastAPI?

easy

A. return PlainTextResponse(content="Hello World")

B. return JSONResponse(content="Hello World")

C. return HTMLResponse(content=123)

D. return FileResponse(path="hello.txt")

Solution

1. Step 1: Identify the correct response class for plain text

   FastAPI provides PlainTextResponse to send plain text content.

2. Step 2: Check the usage syntax

   The correct syntax is to pass the text string as the content argument.

3. Final Answer:

   return PlainTextResponse(content="Hello World") -> Option A

4. Quick Check:

   PlainTextResponse with content string = return PlainTextResponse(content="Hello World") [OK]

Hint: Use PlainTextResponse for text content [OK]

Common Mistakes:

• Using JSONResponse for plain text
• Passing non-string content to HTMLResponse
• Using FileResponse for text content

3. Given the code below, what will be the response content type sent to the client?

from fastapi import FastAPI
from fastapi.responses import HTMLResponse

app = FastAPI()

@app.get("/", response_class=HTMLResponse)
async def read_root():
    return "
Welcome
"

medium

A. text/html

B. application/json

C. text/plain

D. application/octet-stream

Solution

1. Step 1: Identify the response class used

   The route uses response_class=HTMLResponse, which sets the content type to HTML.

2. Step 2: Understand the content type sent

   HTMLResponse sends content with the header Content-Type: text/html.

3. Final Answer:

   text/html -> Option A

4. Quick Check:

   HTMLResponse = text/html content type [OK]

Hint: HTMLResponse sets content type to text/html [OK]

Common Mistakes:

• Assuming JSON is default content type
• Confusing plain text with HTML content type
• Ignoring the response_class parameter

4. What is wrong with this FastAPI endpoint using a custom response class?

from fastapi import FastAPI
from fastapi.responses import JSONResponse

app = FastAPI()

@app.get("/data")
async def get_data():
    return JSONResponse(content=[1, 2, 3], status_code="200")

medium

A. Missing return type annotation

B. content must be a dictionary, not a list

C. JSONResponse cannot be used in async functions

D. status_code should be an integer, not a string

Solution

1. Step 1: Check the status_code argument type

   Status codes must be integers, but here it is passed as a string "200".

2. Step 2: Understand the impact of wrong type

   Passing a string causes a runtime error or unexpected behavior in FastAPI.

3. Final Answer:

   status_code should be an integer, not a string -> Option D

4. Quick Check:

   Status code must be int, not str [OK]

Hint: Use integer for status_code, not string [OK]

Common Mistakes:

• Passing status_code as string
• Thinking content must be dict only
• Believing JSONResponse can't be async

5. You want to create a FastAPI endpoint that returns a CSV file for download using a custom response class. Which approach correctly sets the response to send a CSV file named "report.csv" with content "name,age\nAlice,30"?

hard

A. Use JSONResponse with content as CSV string and set media_type to 'text/csv'

B. Use StreamingResponse with content as bytes and set headers for CSV download

C. Use PlainTextResponse with content as CSV string and no headers

D. Use HTMLResponse with CSV content inside <pre> tags

Solution

1. Step 1: Choose the correct response class for file download

   StreamingResponse is suitable for sending files or streams with custom headers.

2. Step 2: Set content and headers properly

   Content should be bytes, and headers must include Content-Disposition to prompt file download with the filename.

3. Final Answer:

   Use StreamingResponse with content as bytes and set headers for CSV download -> Option B

4. Quick Check:

   StreamingResponse + headers = file download [OK]

Hint: Use StreamingResponse with headers for file downloads [OK]

Common Mistakes:

• Using JSONResponse for CSV files
• Not setting Content-Disposition header
• Using HTMLResponse for file content