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How Do I Return a JSON Response from a Flask View?

James W.

The Problem

You want to get your Flask application to return JSON data in a view response so that you can perform operations on the data. How can you do this?

The Solution

There are two methods you can use to return JSON data in your Flask application’s view: by returning a Python dictionary, or by using Flask’s jsonify() method.

Return a Python Dictionary

If you return a Python dictionary in a Flask view, the dictionary will automatically be converted to the JSON format for the response.

Here is an example of a Flask view that returns a Python dictionary in the JSON format:

from datetime import date

from flask import Flask, jsonify

app = Flask(__name__)


@app.route('/')
def hello_world():
    return {
        "greeting": ["hello", "world"],
        "date": date.today()
    }

This view will return a JSON response that looks like this:

{"date":"Wed, 01 Jun 2022 00:00:00 GMT","greeting":["hello","world"]}

Using jsonify()

The jsonify() method takes either arguments or keyword arguments (using both will not work). These arguments are converted into the JSON format, and will take that format in the views response.

When using single arguments, the values will be treated as a list of values. So jsonify("a", "b", "c") will be treated as jsonify(["a", "b", "c"]).

When using keyword arguments, the data is treated as a dictionary, with the keys representing the keys of the dictionaries and the values representing the values of those keys. So jsonify(a=1, b=2, c=3) is treated as jsonify({"a": 1, "b": 2, "c": 3}).

Here is an example using the jsonify() method to return a dictionary in the JSON format:

from datetime import date

from flask import Flask, jsonify

app = Flask(__name__)


@app.route('/')
def hello_world():
    return jsonify(
        greeting=["hello", "world"],
        date=date.today(),
    )

This view will return a JSON response that looks like this:

{"date":"Wed, 01 Jun 2022 00:00:00 GMT","greeting":["hello","world"]}

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