File download responses in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What Flask function is commonly used to send files for download?

The send_file() function is used in Flask to send files to the client, enabling file downloads.

beginner

How do you specify the filename that the user will see when downloading a file in Flask?

You use the download_name parameter in send_file() to set the filename shown to the user.

beginner

What parameter in send_file() forces the browser to download the file instead of displaying it?

Setting as_attachment=True in send_file() tells the browser to download the file as an attachment.

intermediate

Why is it important to set the correct MIME type when sending a file in Flask?

The MIME type tells the browser what kind of file it is. Setting it correctly helps the browser handle or display the file properly.

intermediate

How can you send a file stored in memory (like a BytesIO object) for download in Flask?

You can pass the in-memory file object directly to send_file() along with as_attachment=True and a download_name.

Which Flask function is used to send a file to the client for download?

A send_file()

B send_response()

C download_file()

D file_send()

The correct function to send files in Flask is send_file().

What parameter do you set to True in send_file() to force a file download?

A as_attachment=True

B download=True

C force_download=True

D attachment=True

Setting as_attachment=True forces the browser to download the file.

How do you specify the filename the user sees when downloading a file in Flask?

A name

B file_name

C filename

D download_name

The download_name parameter sets the filename shown to the user.

If you want to send a PDF file for download, which MIME type should you set?

A text/plain

B image/png

C application/pdf

D application/json

The correct MIME type for PDF files is application/pdf.

Can you use send_file() to send a file stored in memory (like BytesIO)?

A No, only files on disk can be sent

B Yes, by passing the in-memory file object

C Only if you convert it to a string first

D Only if you save it temporarily to disk

You can pass an in-memory file object like BytesIO directly to send_file().

Explain how to send a file for download in Flask including setting the filename and forcing download.

Think about the parameters in send_file() that control download behavior.

Describe why setting the correct MIME type is important when sending files in Flask.

Consider how browsers decide what to do with received files.

Practice

1. What does the as_attachment=True parameter do when used with Flask's send_file function?

easy

A. Encrypts the file before sending it.

B. Changes the file's content type to plain text.

C. Forces the browser to download the file instead of displaying it.

D. Prevents the file from being downloaded.

Solution

1. Step 1: Understand send_file usage

   The send_file function sends files from the server to the client in Flask.

2. Step 2: Role of as_attachment=True

   Setting as_attachment=True tells the browser to download the file instead of trying to open or display it.

3. Final Answer:

   Forces the browser to download the file instead of displaying it. -> Option C

4. Quick Check:

   as_attachment=True means download file [OK]

Hint: Remember: as_attachment=True means download, not display [OK]

Common Mistakes:

• Thinking it changes file content type
• Assuming it encrypts the file
• Believing it blocks download

2. Which of the following is the correct syntax to send a file named 'report.pdf' as a download in Flask?

easy

A. return send_file('report.pdf', as_attachment=True)

B. return send_file('report.pdf', download=True)

C. return send_file('report.pdf', attachment=True)

D. return send_file('report.pdf', force_download=True)

Solution

1. Step 1: Recall correct parameter for download

   The correct parameter to force download is as_attachment=True.

2. Step 2: Check syntax correctness

   return send_file('report.pdf', as_attachment=True) uses send_file('report.pdf', as_attachment=True), which is the correct syntax.

3. Final Answer:

   return send_file('report.pdf', as_attachment=True) -> Option A

4. Quick Check:

   Correct parameter is as_attachment=True [OK]

Hint: Use as_attachment=True to force download in send_file [OK]

Common Mistakes:

• Using incorrect parameter names like download or attachment
• Forgetting to set as_attachment=True
• Using non-existent parameters like force_download

3. What will be the filename suggested to the user when downloading a file with this Flask code?

return send_file('data.csv', as_attachment=True, download_name='user_data.csv')

medium

A. data.csv

B. user_data.csv

C. download_name.csv

D. No filename suggested

Solution

1. Step 1: Understand download_name parameter

   The download_name parameter sets the filename the browser suggests when saving the file.

2. Step 2: Analyze given code

   The code sets download_name='user_data.csv', so the browser will suggest this name.

3. Final Answer:

   user_data.csv -> Option B

4. Quick Check:

   download_name sets saved filename [OK]

Hint: download_name sets the saved filename for downloads [OK]

Common Mistakes:

• Assuming original filename is always used
• Confusing download_name with as_attachment
• Thinking no filename is suggested

4. Identify the error in this Flask code snippet intended to send a file for download:

return send_file('image.png', attachment=True)

medium

A. The parameter should be as_attachment=True, not attachment=True.

B. The filename must be absolute path, not relative.

C. send_file cannot send image files.

D. Missing download_name parameter.

Solution

1. Step 1: Check parameter correctness

   The correct parameter to force download is as_attachment=True, not attachment=True.

2. Step 2: Validate other options

   Relative paths are allowed, images can be sent, and download_name is optional.

3. Final Answer:

   The parameter should be as_attachment=True, not attachment=True. -> Option A

4. Quick Check:

   Correct parameter is as_attachment=True [OK]

Hint: Use as_attachment=True, not attachment=True [OK]

Common Mistakes:

• Using attachment=True instead of as_attachment=True
• Thinking download_name is mandatory
• Believing relative paths are invalid

5. You want to send a PDF file named 'manual.pdf' for download but want the user to save it as 'User_Manual_2024.pdf'. Which Flask code snippet correctly achieves this?

hard

A. return send_file('manual.pdf', as_attachment=True, filename='User_Manual_2024.pdf')

B. return send_file('manual.pdf', as_attachment=False, download_name='User_Manual_2024.pdf')

C. return send_file('manual.pdf', download_name='User_Manual_2024.pdf')

D. return send_file('manual.pdf', as_attachment=True, download_name='User_Manual_2024.pdf')

Solution

1. Step 1: Ensure file is sent as download

   Set as_attachment=True to force download instead of display.

2. Step 2: Set the saved filename

   Use download_name='User_Manual_2024.pdf' to specify the filename suggested to the user.

3. Step 3: Check other options

   return send_file('manual.pdf', as_attachment=False, download_name='User_Manual_2024.pdf') disables download, C misses as_attachment, D uses wrong parameter filename.

4. Final Answer:

   return send_file('manual.pdf', as_attachment=True, download_name='User_Manual_2024.pdf') -> Option D

5. Quick Check:

   Use as_attachment=True and download_name for filename [OK]

Hint: Use as_attachment=True and download_name to rename download [OK]

Common Mistakes:

• Forgetting as_attachment=True disables download
• Using filename instead of download_name
• Setting as_attachment=False causes inline display