Return JSON response from Flask view

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 want to analyze a file uploaded by the user, the Flask quickstart shows how to get files from users and access them. Get the file from request.files and pass it to the summary function.

from flask import request, jsonify
from werkzeug import secure_filename

@app.route('/summary', methods=['GET', 'POST'])
def summary():
    if request.method == 'POST':
        csv = request.files['data']
        return jsonify(
            summary=make_summary(csv),
            csv_name=secure_filename(csv.filename)
        )

    return render_template('submit_data.html')

Replace the 'data' key for request.files with the name of the file input in your HTML form.

Although flask.jsonify is easy to use but I prefer to use a decorator to return json. It helps to returns any json type and is more readable when you have multiple returns in your method. (note that this sample works for 200 responses, I return errors with raising exceptions and Flask.errorhandler)

def return_json(f):
    @functools.wraps(f)
    def inner(*a, **k):
        return json.dumps(f(*a, **k))
    return inner


@app.route('/test/<arg>')
@return_json
def test(arg):
    if arg == 'list':
        return [1, 2, 3]
    elif arg == 'dict':
        return {'a': 1, 'b': 2}
    elif arg == 'bool':
        return True
    return 'non of them'

Although an old question, I thought I'll add this if anyone is looking to return an array of JSONs. Flask 0.10 allows you to do this and it's pretty straightforward.

@app.route('/get_records')
def get_records():
    list = [
        {
          "rec_create_date": "12 Jun 2016",
          "rec_dietary_info": "nothing",
          "rec_dob": "01 Apr 1988",
          "rec_first_name": "New",
          "rec_last_name": "Guy",
        },
        {
          "rec_create_date": "1 Apr 2016",
          "rec_dietary_info": "Nut allergy",
          "rec_dob": "01 Feb 1988",
          "rec_first_name": "Old",
          "rec_last_name": "Guy",
        },
    ]
    return jsonify(results = list)

Like said previously jsonify is the best way or you could also use Flask-responses' package at https://github.com/Parkayun/flask-responses

@app.route("/json")
def hello():
    return json_response(your_dict, status_code=201)