How to write a simple Flask API for hello world?

Prerequisites: Introduction to REST API

REST stands for Representational State Transfer and is an architectural style used in modern web development. It defines a set of rules/constraints for a web application to send and receive data. In this article, we are going to learn how to create a simple REST API that returns ‘Hello World’, with the help of a flask.

In this article we are going to write a simple flask API for hello world using two methods:

• Using Flask jsonify object.
• Using the flask_restful library with Flask.

Installation

1. Install the python Flask library using the following command.

pip install Flask

2. Install the flask-restful library using the following command.

pip install Flask-RESTful

Method 1: Using Flask ‘jsonify’ object

• 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.

Python3

app =   Flask(__name__)

• Create a new function named ‘helloworld’. This function is going to return the ‘Hello World’ text in JSON format.
• Route the ‘helloworld’ function to your desired URL using the following syntax.

Python3

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

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

Python3

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

• Run the ‘main.py’ file in the terminal or the IDE and type the following URL in the browser.

http://127.0.0.1:5000/hello

Code :

Python3

from flask import Flask, jsonify, request

app = Flask(__name__)


@app.route('/hello', methods=['GET'])
def helloworld():
    if(request.method == 'GET'):
        data = {"data": "Hello World"}
        return jsonify(data)


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

Output :

Method 2: Using the flask_restful library 

• 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 a app variable using the following syntax.

Python3

app =   Flask(__name__)

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

Python3

api =   Api(app)

• Create a resource class named ‘HelloWorld’.
• Inside the resource class, create a ‘get’ method.
• Return a dictionary with the ‘Hello World’ message from the ‘get’ method.
• Add the resource class to the API using the add_resource method.
• Build the flask application using the following command.

Python3

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

• Run the ‘main.py’ file in the terminal or the IDE and type the following URL in the browser.

http://127.0.0.1:5000/hello

Code :

Python3

from flask import Flask
from flask_restful import Api, Resource

app =   Flask(__name__)

api =   Api(app)

class HelloWorld(Resource):
    def get(self):
        data={"data":"Hello World"}
        return data

api.add_resource(HelloWorld,'/hello')


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

Output :