How to return a JSON response from a Flask API ?

Flask is one of the most widely used python micro-frameworks to design a REST API. In this article, we are going to learn how to create a simple REST API that returns a simple JSON object, with the help of a flask.

Prerequisites: Introduction to REST API

What is a REST API?

REST stands for Representational State Transfer and is an architectural style used in modern web development. It defines a set or rules/constraints for a web application to send and receive data. In this article, we will build a REST API in Python using the Flask framework. Flask is a popular micro framework for building web applications.

Approaches: We are going to write a simple flask API that returns a JSON response using two approaches:

1. Using Flask jsonify object.
2. Using the flask_restful library with Flask.

Libraries Required:

• Install the python Flask library using the following command:

pip install Flask

• Install the flask-restful library using the following command:

pip install Flask-RESTful

Approach 1: Using Flask jsonify object – In this approach, we are going to return a JSON response using the flask jsonify method. We are not going to use the flask-restful library in this method.

• Create a new python file named ‘main.py’.
• import Flask, jsonify, and request from the flask framework.
• Register the web app into an app variable using the following syntax.

app = Flask(__name__)

• Create a new function named ‘ReturnJSON’. This function is going to return the sample JSON response.
• Route the ‘ReturnJSON’ function to your desired URL using the following syntax.

@app.route('/path_of_the_response', methods = ['GET'])
def ReturnJSON():
  pass

• Inside the ‘ReturnJSON’ function if the request method is ‘GET’ then create a python dictionary with the two elements message.
• Jsonify the python dictionary and return it.
• Build the flask application using the following command.

if __name__=='__main__':
    app.run(debug=True)

• Run the ‘main.py’ file in the terminal or the IDE.

Code:

Python3

from flask import Flask,jsonify,request

app =   Flask(__name__)

@app.route('/returnjson', methods = ['GET'])
def ReturnJSON():
    if(request.method == 'GET'):
        data = {
            "Modules" : 15,
            "Subject" : "Data Structures and Algorithms",
        }

        return jsonify(data)

if __name__=='__main__':
    app.run(debug=True)

Output:

Approach 2: Using the flask_restful library with Flask – In this approach, we are going to create a simple JSON response with the help of the flask-restful library. The steps are discussed below:

• Create a new python file named ‘main.py’.
• Import Flask from the flask framework.
• Import API and Resource from the ‘flask_restful’ library.
• Register the web app into an app variable using the following syntax.

app = Flask(__name__)

• Register the app variable as an API object using the API method of the ‘flask_restful’  library.

api = Api(app)

• Create a resource class named ‘ReturnJSON’.
• Inside the resource, the class creates a ‘get’ method.
• Return a dictionary with the simple JSON response from the ‘get’ method.
• Add the resource class to the API using the add_resource method.
• Build the flask application using the following command.

if __name__=='__main__':
    app.run(debug=True)

• Run the ‘main.py’ file in the terminal or the IDE.

Code:

Python3

from flask import Flask
from flask_restful import Api, Resource

app =   Flask(__name__)

api =   Api(app)

class returnjson(Resource):
    def get(self):
        data={
            "Modules": 15,
            "Subject": "Data Structures and Algorithms"
        }
        return data

api.add_resource(returnjson,'/returnjson')


if __name__=='__main__':
    app.run(debug=True)

Output: