File responses in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this FastAPI endpoint return?

Consider this FastAPI endpoint that uses FileResponse to send a file to the client. What will the client receive when accessing this endpoint?

FastAPI

from fastapi import FastAPI
from fastapi.responses import FileResponse

app = FastAPI()

@app.get('/download')
async def download_file():
    return FileResponse('example.txt', media_type='text/plain', filename='downloaded.txt')

A The client downloads the file 'example.txt' but it is saved as 'downloaded.txt' on the client side.

B The client gets a JSON response describing the file 'example.txt'.

C The client receives the content of 'example.txt' displayed as plain text in the browser.

D The client receives a 404 error because FileResponse cannot find 'example.txt'.

💡 Hint

Think about what the filename parameter does in FileResponse.

The FileResponse sends the file content as a downloadable file. The filename parameter sets the name suggested to the client for saving the file. So the client downloads the content of 'example.txt' but the saved file name is 'downloaded.txt'.

📝 Syntax

intermediate

Identify the syntax error in this FastAPI file response code

Which option contains a syntax error that will prevent the FastAPI app from running?

FastAPI

from fastapi import FastAPI
from fastapi.responses import FileResponse

app = FastAPI()

@app.get('/file')
async def get_file():
    return FileResponse('data.csv', media_type='text/csv', filename='data.csv')

A return FileResponse('data.csv')

B return FileResponse('data.csv', media_type='text/csv', filename='data.csv')

C return FileResponse('data.csv', media_type='text/csv')

D return FileResponse('data.csv', media_type='text/csv' filename='data.csv')

💡 Hint

Look carefully at the commas between arguments.

Option D is missing a comma between media_type='text/csv' and filename='data.csv', causing a syntax error.

🔧 Debug

advanced

Why does this FastAPI FileResponse raise a FileNotFoundError?

This FastAPI endpoint raises a FileNotFoundError when accessed. What is the most likely cause?

FastAPI

from fastapi import FastAPI
from fastapi.responses import FileResponse

app = FastAPI()

@app.get('/getfile')
async def get_file():
    return FileResponse('files/report.pdf')

A The file 'files/report.pdf' does not exist at the specified path.

B FileResponse requires an absolute path, relative paths cause FileNotFoundError.

C The media_type parameter is missing, causing the error.

D FastAPI does not support serving PDF files with FileResponse.

💡 Hint

Check if the file path is correct and the file exists.

FileResponse raises FileNotFoundError if the file path is invalid or the file does not exist. Relative paths are allowed if the file exists relative to the working directory.

❓ state_output

advanced

What is the Content-Disposition header value sent by this FileResponse?

Given this FastAPI endpoint, what will be the exact Content-Disposition header value in the HTTP response?

FastAPI

from fastapi import FastAPI
from fastapi.responses import FileResponse

app = FastAPI()

@app.get('/download')
async def download():
    return FileResponse('image.png', filename='picture.png')

A inline; filename=image.png

B attachment; filename=picture.png

C attachment; filename=image.png

D inline; filename=picture.png

💡 Hint

FileResponse sets Content-Disposition to attachment by default when filename is provided.

When the filename parameter is set, FileResponse sets the Content-Disposition header to attachment; filename=... to prompt download with that filename.

🧠 Conceptual

expert

Which option correctly streams a large file efficiently with FastAPI?

You want to serve a very large file without loading it fully into memory. Which FastAPI FileResponse usage is best for this?

A return FileResponse('largefile.zip')

B return FileResponse(open('largefile.zip', 'rb'))

C return FileResponse('largefile.zip', media_type='application/zip', filename='largefile.zip')

D return FileResponse('largefile.zip', chunk_size=1024*1024)

💡 Hint

Consider how FileResponse handles file streaming and metadata.

Option C correctly uses FileResponse with the file path, sets media_type and filename. FileResponse streams the file efficiently by default. Option C passes a file object which is not supported. Option C uses a non-existent chunk_size parameter. Option C lacks media_type and filename metadata.