JSON response formatting in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of using jsonify in Flask?

The jsonify function formats Python data structures into a JSON response with the correct content type application/json. It helps send data to the client in a standard JSON format.

beginner

How do you return a JSON response with a custom status code in Flask?

Use jsonify(data), status_code. For example, return jsonify({'message': 'ok'}), 201 sends JSON with HTTP status 201.

beginner

What content type does Flask set automatically when using jsonify?

Flask sets the content type to application/json automatically when you use jsonify. This tells the browser or client that the response is JSON data.

intermediate

Why should you avoid returning a plain Python dictionary directly from a Flask route?

Returning a plain dictionary does not set the content type to JSON automatically. This can cause clients to misinterpret the response. Using jsonify ensures proper JSON formatting and headers.

intermediate

How can you include custom headers in a JSON response in Flask?

Create the response with jsonify, then use response.headers['Header-Name'] = 'value'. Finally, return the response object.

Which Flask function is best for sending JSON responses?

A jsonify

B render_template

C redirect

D send_file

jsonify formats data as JSON and sets the correct content type.

What content type does jsonify set in the response?

A application/json

B text/html

C text/plain

D application/xml

jsonify sets application/json to indicate JSON data.

How do you return a JSON response with status code 404 in Flask?

A return render_template('404.html'), 404

B return {'error': 'Not found'}, 404

C return jsonify({'error': 'Not found'}), 404

D return redirect('/404')

Use jsonify with the status code to send JSON and HTTP status.

What happens if you return a plain dictionary from a Flask route?

A Flask automatically converts it to JSON

B Flask returns it as plain text without JSON headers

C Flask raises an error

D Flask redirects to another page

Returning a dict directly does not set JSON content type, so clients may not parse it as JSON.

How can you add a custom header to a JSON response in Flask?

A Add header to the dictionary before jsonify

B Custom headers are not allowed in JSON responses

C Pass headers as a second argument to jsonify

D Use <code>response.headers['Name'] = 'value'</code> on the response object

You modify the response object headers after calling jsonify.

Explain how to send a JSON response with a custom HTTP status code in Flask.

Think about how Flask routes return data and status.

Describe why using jsonify is better than returning a plain dictionary in Flask routes.

Consider how browsers and clients understand response data.