Simple restful api demo.py

General steps
1. import necessary libraries

2. initialize app and api
   use app = Flask(__name__)
   and api = Api(app)

3. define class ToDo(Resource), inherit Resouce, in the class we can further defien methods such as post, get...
   class Todo(Resource)>
        def get():
            
        def post():
            
4. use api.add_resource ass routes, corresponding to url
   api.add_resource(ToDo, "/todo")

    
1. import necessary libraries
from flask import Flask, jsonify, request
from flask_restful import Api, Resource

2. initialize app and api
app = Flask(__name__)
api = Api(app)


def checkPostedData(postedData, functionName):
    if (functionName == "add" or functionName == "subtract" or functionName == "multiply"):
        if "x" not in postedData or "y" not in postedData:
            return 301 #Missing parameter
        else:
            return 200
    elif (functionName == "division"):
        if "x" not in postedData or "y" not in postedData:
            return 301
        elif int(postedData["y"])==0:
            return 302
        else:
            return 200

3. define class ToDo(Resource), inherit Resouce, in the class we can further defien methods such as post, get...
class Add(Resource):
    def post(self):
        #If I am here, then the resouce Add was requested using the method POST

        #Step 1: Get posted data:
        postedData = request.get_json()

        #Steb 1b: Verify validity of posted data
        status_code = checkPostedData(postedData, "add")
        if (status_code!=200):
            retJson = {
                "Message": "An error happened",
                "Status Code":status_code
            }
            return jsonify(retJson)

        #If i am here, then status_code == 200
        x = postedData["x"]
        y = postedData["y"]
        x = int(x)
        y = int(y)

        #Step 2: Add the posted data
        ret = x+y
        retMap = {
            'Message': ret,
            'Status Code': 200
        }
        return jsonify(retMap)

class Subtract(Resource):
    def post(self):
        #If I am here, then the resouce Subtract was requested using the method POST

        #Step 1: Get posted data:
        postedData = request.get_json()

        #Steb 1b: Verify validity of posted data
        status_code = checkPostedData(postedData, "subtract")


        if (status_code!=200):
            retJson = {
                "Message": "An error happened",
                "Status Code":status_code
            }
            return jsonify(retJson)

        #If i am here, then status_code == 200
        x = postedData["x"]
        y = postedData["y"]
        x = int(x)
        y = int(y)

        #Step 2: Subtract the posted data
        ret = x-y
        retMap = {
            'Message': ret,
            'Status Code': 200
        }
        return jsonify(retMap)


class Multiply(Resource):
    def post(self):
        #If I am here, then the resouce Multiply was requested using the method POST

        #Step 1: Get posted data:
        postedData = request.get_json()

        #Steb 1b: Verify validity of posted data
        status_code = checkPostedData(postedData, "multiply")


        if (status_code!=200):
            retJson = {
                "Message": "An error happened",
                "Status Code":status_code
            }
            return jsonify(retJson)

        #If i am here, then status_code == 200
        x = postedData["x"]
        y = postedData["y"]
        x = int(x)
        y = int(y)

        #Step 2: Multiply the posted data
        ret = x*y
        retMap = {
            'Message': ret,
            'Status Code': 200
        }
        return jsonify(retMap)

class Divide(Resource):
    def post(self):
        #If I am here, then the resouce Divide was requested using the method POST

        #Step 1: Get posted data:
        postedData = request.get_json()

        #Steb 1b: Verify validity of posted data
        status_code = checkPostedData(postedData, "division")


        if (status_code!=200):
            retJson = {
                "Message": "An error happened",
                "Status Code":status_code
            }
            return jsonify(retJson)

        #If i am here, then status_code == 200
        x = postedData["x"]
        y = postedData["y"]
        x = int(x)
        y = int(y)

        #Step 2: Multiply the posted data
        ret = (x*1.0)/y
        retMap = {
            'Message': ret,
            'Status Code': 200
        }
        return jsonify(retMap)

4. use api.add_resource ass routes, corresponding to url
api.add_resource(Add, "/add")
api.add_resource(Subtract, "/subtract")
api.add_resource(Multiply, "/multiply")
api.add_resource(Divide, "/division")

@app.route('/')
def hello_world():
    return "Hello World!"


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