A simple HTTP-API with Flask

• In this repo we create a simple Flask HTTP API that calculate sum of two values from a JSON input and outputs the sum in the JSON format.
• All is done in Python and you can apply the method used here to any other complex application and formulas that need to run a Python code in the Backend.

1. Step 1 (create a directory)
2. Step 2 (setting up the environment)
3. Step 3 (installing Flask)
4. Step 4 (Python code and Flask)
5. Step 5 (test)

Make a repository or directory in your local machine: lets call it flask-app/

flask-app/
│
├──
│
└── 

Navigate to your app directory and create and activate a virtual environment to make sure that installing libraries doesn't break your other apps:

$ python -m venv venv
$ source venv/bin/activate

Now you have a venv/ directory inside your app directory.

flask-app/
│
├
│
└── venv/

Install Flask using:

$ pip instal flask

to make sure that Flask is installed: call the Python prompt by typing:

$ python

and then running the following:

import flask
print(flask.__version__)

if it gives you the version, then it's installed correctly in your environment.

Create a Python file in your directory and call it something like flask-app1.py. You should have now all of these in your main directory:

flask-app/
│
├── flask-app1.py
│
└── venv/

Modify the Python file .py with adding the following code to it:

@app.route('/sum', methods=['POST'])

• This is basically creating a http endpoint for getting the JSON

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

@app.route('/sum', methods=['POST'])
def  sum():
	data = request.get_json()
	a = data['a']
	b = data['b']
	result = a + b
return  jsonify(result=result)

if  __name__ == '__main__':
	app.run(port=8000)

Now we can test it whether our app works well or not:

• It should gives us the JSON output of 8 for a JSON input of 3, 5: '{"a":5, "b":3}'

To do so run the following command in the shell to run the app first:

$ python flask-app1.py

It should run a server on http:https://127.0.0.1:8000 and then you can make a JSON request like:

curl -X POST -H "Content-Type: application/json" -d '{"a":5, "b":3}' http:https://localhost:8000/sum

It should show the result as a JSON output like**{"result":8}** in the shell:

{"result":8}

After testing your app make sure your are shutting down the server by pressing ctrl+C. Finally deactivate your environment using:

$ deactivate