Return JSON response from Flask view

A view can directly return a Python dict or list and Flask will call jsonify automatically.

@app.route("/summary")
def summary():
    d = make_summary()
    return d

For older Flask versions, or to return a different JSON-serializable object, import and use jsonify.

from flask import jsonify

@app.route("/summary")
def summary():
    d = make_summary()
    return jsonify(d)

jsonify serializes the data you pass it to JSON. If you want to serialize the data yourself, do what jsonify does by building a response with status=200 and mimetype='application/json'.

from flask import json

@app.route('/summary')
def summary():
    data = make_summary()
    response = app.response_class(
        response=json.dumps(data),
        status=200,
        mimetype='application/json'
    )
    return response

Pass keyword arguments to flask.jsonify and they will be output as a JSON object.

@app.route('/_get_current_user')
def get_current_user():
    return jsonify(
        username=g.user.username,
        email=g.user.email,
        id=g.user.id
    )

{
    "username": "admin",
    "email": "admin@localhost",
    "id": 42
}

If you already have a dict, you can pass it directly as jsonify(d).

If you don't want to use jsonify for some reason, you can do what it does manually. Call flask.json.dumps to create JSON data, then return a response with the application/json content type.

from flask import json

@app.route('/summary')
def summary():
    data = make_summary()
    response = app.response_class(
        response=json.dumps(data),
        mimetype='application/json'
    )
    return response

flask.json is distinct from the built-in json module. It will use the faster simplejson module if available, and enables various integrations with your Flask app.