Notes

29. Using Flask to Build RESTful APIs and Generate Web Services
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A well-liked micro-framework for Python web application development is called Flask. It is flexible, lightweight, and simple to use. Building RESTful APIs and web services that can interface with other apps or clients is one of the most popular uses for Flask.
What is a RESTful API?
The web application design paradigm known as REST stands for REpresentational State Transfer. It lays out a set of guidelines and limitations for data transmission and reception via the internet for web applications. Among the fundamental ideas of REST are:
— Resource-oriented: Any entity that can be uniquely recognized by a URL is a resource, and resources make up a web application. A resource might be, for instance, a person, a product, a blog article, etc.
— Stateless: Every request that a client sends to a server has to include all the data required to fulfill the request. Client state or session data is not stored on the server. As a result, the web application is more dependable and scalable.
— Uniform interface: To communicate with the resources, the web application employs a set of common protocols and formats. The most often used methods are CRUD (Create, Read, Update, Delete) (GET, POST, PUT, and DELETE), which relate to the actions on the resources. The most widely used data transfer format is JSON (JavaScript Object Notation), which is simple to use and legible by humans.
— HATEOAS (Hypermedia as the Engine of Application State): The client can dynamically explore the web application and find new features by following the connections to relevant resources that are provided in the response.
How to create a RESTful API using Flask?
There are two approaches to use Flask to construct a RESTful API: either use the flask_restful extension or use Flask without any extra libraries. The decision between the two methods relies on the intricacy and specifications of the web application, since each has advantages and disadvantages.
Using Flask without any external libraries
This method works well for small-scale, basic web apps that don’t require a lot of customisation or sophisticated features. The fundamental actions are:
— From the flask module, import Flask and jsonify. The primary class for the web application is called Flask, and the utility method jsonify is used to transform a Python object into a JSON response.
— Make a Flask class instance and attach it to the app variable. This is the web application’s primary entrance point.
— To specify the methods that are permitted for each route and the URL routes for the resources, use the app.route decorator. The URL path and a list of methods are the two inputs that the decorator accepts. Angle-bracketed variable portions, like int:num, can appear in the URL route. The view function handling the request has access to these variable components as arguments.
— Specify the view functions for each route that deal with the requests. The request object, which includes the request’s headers, query parameters, content, and other details, is what the view functions take as an input. To access and handle the request data, the view functions can make use of the request.method, request.args, request.form, request.json, and other request methods and properties. The flask module’s jsonify and make_response methods may be used to construct the response object that the view functions need to return. The response content, headers, and status code may all be found in the response object.
— The app.run function, which accepts optional parameters like debug, port, host, etc., may be used to launch the web application. The debug mode, which offers helpful data and tools for testing and development such error messages, stack traces, and an online debugger, is enabled via the debug parameter.
Here is an example of a simple RESTful API that returns the square of a number using Flask without any external libraries:
from flask import Flask, jsonify, requestapp = Flask(__name__)@app.route('/', methods=['GET', 'POST'])def home(): if request.method == 'GET': data = 'hello world' return jsonify('data': data) elif request.method == 'POST': data = request.get_json() return jsonify('data': data), [email protected]('/square/<int:num>', methods=['GET'])def square(num): return jsonify('square': num**2)if __name__ == '__main__': app.run(debug=True) Using flask_restful
Large-scale, intricate web applications that require extensive customisation and cutting-edge functionality are a good fit for this methodology. A collection of classes and utilities called flask_restful make it easier and more enjoyable to create RESTful APIs using Flask. The following are some advantages of using flask_restful:
— Resource-oriented: The resources in the web application are classes that derive from the flask_restful module’s Resource class. Every resource can have several methods connected with it, similar to the HTTP methods: get, post, put, delete, etc. The resource methods produce a Python object that is automatically transformed into a JSON response, taking the request object as an input.
— Automatic routing: It is not necessary for the web application to manually declare the URL routes for every resource. Alternatively, the web application can make use of the Flask class’s wrapper, the Api class from the flask_restful module, which offers more capabilities and functionalities. The add_resource function of the Api class registers the resource methods for the associated URL route automatically by accepting a resource class and a URL path as inputs. Variable elements that are supplied as arguments to the resource methods can also be found in the URL path.
— Request parsing: The flask_restful module’s reqparse module, which offers a RequestParser class that can parse and validate the request data, may be used by the web application. The add_argument method of the RequestParser class accepts the name of the request argument along with other optional arguments like type, required, help, location, etc. The parse_args function of the RequestParser class yields a dictionary containing the request parameters that satisfy the requirements.
— Output formatting: The flask_restful module’s marshal and fields modules offer a method for formatting and filtering the output data, which the web application may utilize. A collection of field classes, including String, Integer, Boolean, Nested, List, etc., are provided by the fields module and specify how the output data should be serialized. A JSON object that complies with the fields standard is returned by the marshal function, which is provided by the marshal module. It accepts three parameters: a Python object, a dictionary of fields, and an optional envelope.
Here is an example of a RESTful API that returns the square of a number using flask_restful:
from flask import Flask, requestfrom flask_restful import Resource, Api, reqparse, marshal, fieldsapp = Flask(__name__)api = Api(app)class Hello(Resource): def get(self): return 'message': 'hello world' def post(self): data = request.get_json() return 'data': data, 201class Square(Resource): def get(self, num): return 'square': num**2api.add_resource(Hello, '/')api.add_resource(Square, '/square/<int:num>')if __name__ == '__main__': app.run(debug=True) Resources:
Python | Build a REST API using Flask — GeeksforGeeksBuilding REST APIs with Flask: Create Python Web Services with MySQL | SpringerLinkCreate a RESTful API Using Python and Flask | Linode DocsBuilding RESTful APIs With Flask: The DIY Approach | Envato Tuts+ (tutsplus.com)How to Create a RESTful API with Flask in Python — Python Code (thepythoncode.com)Stackademic Thank you for reading until the end. Before you go:
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