About a week back I had asked some of my juniors to build a flask app. The result was a mixture of classes and  Resource implementation of flask_restful library. When asked why they made it so complex, he showed me the google search results for – how to build REST API’s using flask. Almost all the tutorials out there are either too in-depth or too difficult for beginners.This post is a beginner friendly tutorial on how to build flask API’s.

Before we start – a few jargon.
Flask: is a Python-based microframework that enables you to build web applications. The “micro” in microframework means Flask aims to keep the core simple but extensible.

REST: a RESTful API uses HTTP requests to GET, PUT, POST and DELETE data.

RESTful API designing: guidelines is a must read before you continue. It talks about terminologies, endpoints, versioning status codes and so much more.

Routing

Let’s take this program snippet for example –

Using @app.route you define which function will run when a particular endpoint(URL) is called. Inside the route decorator you can define the API endpoint, the methods that will activate the function below it.

URL patterns

In the above example, the <username> can be anything. A variable, that is used as a parameter for the function below the decorator. This is one of the ways using which you can pass variables from your front-end to your backend.

GET request

The following snippet creates an API to recieve 2 numbers and return their sum.

Using URL parameters: eg – http://127.0.0.1:5000/?num1=2&num2=40

The same task using form data –

And the same using json data –

You can use the above examples with different types of request types by changing the method’s parameter.

Handling GET and POST request in the same function