Python – Make a simple API with Flask and Postman

Flask is actually really a powerful tool for making an API. In the video below, you would see how quickly I am building an API, that does four really simple functions.

The functions are – saying “Hello”, multiplying a number by itself 2 times (e.g. cubing a number), concatenating 2 strings and just returning twice any given string. Nothing fancy, but if this is the first time you are seeing Flask, API and Python I hope it would be useful!

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route('/api/testapi', methods=['POST'])
def testapi():
    data = request.get_json()
    print(f'{data}{data}')
    return f'{data}{data}'

@app.route('/api/greet', methods=['POST'])
def greet():
    data = request.get_json()

    if 'name' not in data:
        return jsonify({'error':'Required - name!'}), 400

    name = data['name']
    greeting = f"Hello, there - {name}!"

    return jsonify({'message':greeting})

@app.route('/api/cube', methods=['POST'])
def cube():
    data = request.get_json()
    #print("\nMultiplying 3 times the same value!")
    if 'number' not in data:
        return jsonify({'error':'Required - number!'}), 400

    number = data['number']
    result = number ** 3

    return jsonify({'result': result})


@app.route('/api/concat', methods=['POST'])
def concat():
    data = request.get_json()

    if ('string1' not in data) or ('string2' not in data):
        return jsonify({'error':'Required - string1 and string2!'}), 400

    string1 = data['string1']
    string2 = data['string2']
    result = string1 + string2

    return jsonify({'result': result})



if __name__ == '__main__':
    app.run(debug=True)

Additionally, there are 3 tests for the “cube” function:

import unittest
import json
from app import app

class TestApp(unittest.TestCase):

    def setUp(self):
        self.app = app.test_client()
        self.app.testing = True

    def test_cube_endpoint(self):
        data = {"number": 5}
        response = self.app.post('/api/cube', json=data)
        result = json.loads(response.data.decode('utf-8'))
        self.assertEqual(response.status_code, 200)
        self.assertEqual(result['result'], 125)

    def test_cube_negative_number(self):
        data = {"number": -3}
        response = self.app.post('/api/cube', json=data)
        result = json.loads(response.data.decode('utf-8'))
        self.assertEqual(response.status_code, 200)
        self.assertEqual(result['result'], -27)

    def test_cube_missing_number(self):
        data = {}
        response = self.app.post('/api/cube', json=data)
        result = json.loads(response.data.decode('utf-8'))
        self.assertEqual(response.status_code, 400)
        self.assertIn('error', result)
    
if __name__ == '__main__':
    unittest.main()

To run the tests, enter in the terminal python test_app.py.

To run the API, enter in the terminal python app.py.

And I hope you have enjoyed the video! 🙂