restshop.py

from flask import Flask, jsonify, request

app = Flask(__name__)

shop = [
    {
        "id": 1,
        "title": "Java",
        "available": 8
    },
    {
        "id": 2,
        "title": "C++",
        "available": 7
    },
    {
        "id": 3,
        "title": "Python",
        "available": 6
    }
]

@app.route("/products")
def list_products():
    return jsonify( {"products:" : shop } )

@app.route("/invoice", methods = ["POST"] )
def buy():
    id = request.json["id"]
    for product in shop:
        if product["id"] == id:
            product["available"] = product["available"] - 1
            return jsonify( { "status" : "OK" })

    return jsonify( {"status" : "rejected" }), 400

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