Python | Build a REST API using Flask

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.

# 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.

# 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) 

Output:

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Libraries required:

Method 1: using only Flask

Method 2: Using flask-restful

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