Building a simple API to add two numbers

Now we will build a very simple API to get a grip on the Flask library and framework. This API will accept a JSON object with two numbers and return the sum of the numbers as a response.

Open a new notebook from your Jupyter home page:

1. Import all the libraries we need and create an app instance:

from flask import Flask, request 
app = Flask(__name__)

1. Create the index page for the RESTful API using the route() decorator:

@app.route('/') 
def hello_world(): 
 return 'This is the Index page'

1. Create a POST API to add two numbers using the route() decorator. This API accepts a JSON object with the numbers to be added:

@app.route('/add', methods=['POST']) 
def add(): 
    req_data = request.get_json() 
    number_1 = req_data['number_1'] 
    number_2 = req_data['number_2'] 
    return str(int(number_1)+int(number_2))

Save the Python notebook and use the File menu to download the notebook as a Python file. Place the Python file in the same directory as the model file.

Start a new command terminal and traverse to the folder with this Python file and the model. Make sure to activate the conda environment and run the following to start a server running the simple API:

• If you are using Windows, enter the following:

set FLASK_APP=simple_api

• If you aren't using Windows, enter this:

export FLASK_APP=simple_api

Then type the following:

flask run

You should see the following output when the server starts:

Open the browser and paste this address in the URL bar to go to the index page: http://127.0.0.1:5000/. Here is the output:

Next, we will use curl to access the POST API that adds two numbers. Open a new terminal and enter the following curl command to test the /add API. The numbers to add in this example are 1 and 2, and this is passed as a JSON object:

curl -i -X POST -H "Content-Type: application/json" -d "{\"number_1\":\"1\",\"number_2\":\"2\"}" http://127.0.0.1:5000/add

We will get a response with the sum of the numbers if there are no errors:

The complete code for the simple API is available as a Python notebook named simple_api.ipynb and as a Python file named simple_api.py.