Python | Build a REST API using Flask

Last Updated : 25 Feb, 2022

Prerequisite: Introduction to 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. Since it is a micro-framework, it is very easy to use and lacks most of the advanced functionality which is found in a full-fledged framework. Therefore, building a REST API in Flask is very simple. There are two ways of creating a REST API in Flask:

Using Flask without any external libraries
Using flask_restful library

Libraries required:

flask_restful can be installed via the pip command:

 sudo pip3 install flask-restful

Method 1: using only Flask

Here, there are two functions: One function to just return or print the data sent through GET or POST and another function to calculate the square of a number sent through GET request and print it.

python3 1==

# Using flask to make an api # import necessary libraries and functions from flask import Flask, jsonify, request # creating a Flask app app = Flask(__name__) # on the terminal type: curl http://127.0.0.1:5000/ # returns hello world when we use GET. # returns the data that we send when we use POST. @app.route('/', methods = ['GET', 'POST']) def home():  if(request.method == 'GET'):  data = "hello world"  return jsonify({'data': data}) # A simple function to calculate the square of a number # the number to be squared is sent in the URL when we use GET # on the terminal type: curl http://127.0.0.1:5000 / home / 10 # this returns 100 (square of 10) @app.route('/home/<int:num>', methods = ['GET']) def disp(num):  return jsonify({'data': num**2}) # driver function if __name__ == '__main__':  app.run(debug = True)

Output:

Executing the square function:

Method 2: Using flask-restful

Flask Restful is an extension for Flask that adds support for building REST APIs in Python using Flask as the back-end. It encourages best practices and is very easy to set up. Flask restful is very easy to pick up if you're already familiar with flask. In flask_restful, the main building block is a resource. Each resource can have several methods associated with it such as GET, POST, PUT, DELETE, etc. for example, there could be a resource that calculates the square of a number whenever a get request is sent to it. Each resource is a class that inherits from the Resource class of flask_restful. Once the resource is created and defined, we can add our custom resource to the api and specify a URL path for that corresponding resource.

python3 1==

# using flask_restful from flask import Flask, jsonify, request from flask_restful import Resource, Api # creating the flask app app = Flask(__name__) # creating an API object api = Api(app) # making a class for a particular resource # the get, post methods correspond to get and post requests # they are automatically mapped by flask_restful. # other methods include put, delete, etc. class Hello(Resource):  # corresponds to the GET request.  # this function is called whenever there  # is a GET request for this resource  def get(self):  return jsonify({'message': 'hello world'})  # Corresponds to POST request  def post(self):    data = request.get_json() # status code  return jsonify({'data': data}), 201 # another resource to calculate the square of a number class Square(Resource):  def get(self, num):  return jsonify({'square': num**2}) # adding the defined resources along with their corresponding urls api.add_resource(Hello, '/') api.add_resource(Square, '/square/<int:num>') # driver function if __name__ == '__main__':  app.run(debug = True)