A example API using Flask

flask_api.py

from flask import Flask
from flask_restful import Resource, Api, reqparse
import pandas as pd
import ast

app = Flask(__name__)
api = Api(app)

class Users(Resource):
    def get(self):
        data = pd.read_csv('users.csv')  # read local CSV
        data = data.to_dict()  # convert dataframe to dict
        return {'data': data}, 200  # return data and 200 OK

    def post(self):
        parser = reqparse.RequestParser()  # initialize
        parser.add_argument('userId', required=True)  # add args
        parser.add_argument('name', required=True)
        parser.add_argument('city', required=True)
        args = parser.parse_args()  # parse arguments to dictionary

        # read our CSV
        data = pd.read_csv('users.csv')

        if args['userId'] in list(data['userId']):
            return {
                'message': f"'{args['userId']}' already exists."
            }, 409
        else:
            # create new dataframe containing new values
            new_data = pd.DataFrame({
                'userId': [args['userId']],
                'name': [args['name']],
                'city': [args['city']],
                'locations': [[]]
            })
            # add the newly provided values
            data = data.append(new_data, ignore_index=True)
            data.to_csv('users.csv', index=False)  # save back to CSV
            return {'data': data.to_dict()}, 200  # return data with 200 OK

    def put(self):
        parser = reqparse.RequestParser()  # initialize
        parser.add_argument('userId', required=True)  # add args
        parser.add_argument('location', required=True)
        args = parser.parse_args()  # parse arguments to dictionary

        # read our CSV
        data = pd.read_csv('users.csv')
        
        if args['userId'] in list(data['userId']):
            # evaluate strings of lists to lists !!! never put something like this in prod
            data['locations'] = data['locations'].apply(
                lambda x: ast.literal_eval(x)
            )
            # select our user
            user_data = data[data['userId'] == args['userId']]

            # update user's locations
            user_data['locations'] = user_data['locations'].values[0] \
                .append(args['location'])
            
            # save back to CSV
            data.to_csv('users.csv', index=False)
            # return data and 200 OK
            return {'data': data.to_dict()}, 200

        else:
            # otherwise the userId does not exist
            return {
                'message': f"'{args['userId']}' user not found."
            }, 404

    def delete(self):
        parser = reqparse.RequestParser()  # initialize
        parser.add_argument('userId', required=True)  # add userId arg
        args = parser.parse_args()  # parse arguments to dictionary
        
        # read our CSV
        data = pd.read_csv('users.csv')
        
        if args['userId'] in list(data['userId']):
            # remove data entry matching given userId
            data = data[data['userId'] != args['userId']]
            
            # save back to CSV
            data.to_csv('users.csv', index=False)
            # return data and 200 OK
            return {'data': data.to_dict()}, 200
        else:
            # otherwise we return 404 because userId does not exist
            return {
                'message': f"'{args['userId']}' user not found."
            }, 404

                    
class Locations(Resource):
    def get(self):
        data = pd.read_csv('locations.csv')  # read local CSV
        return {'data': data.to_dict()}, 200  # return data dict and 200 OK
    
    def post(self):
        parser = reqparse.RequestParser()  # initialize parser
        parser.add_argument('locationId', required=True, type=int)  # add args
        parser.add_argument('name', required=True)
        parser.add_argument('rating', required=True)
        args = parser.parse_args()  # parse arguments to dictionary
        
        # read our CSV
        data = pd.read_csv('locations.csv')
    
        # check if location already exists
        if args['locationId'] in list(data['locationId']):
            # if locationId already exists, return 401 unauthorized
            return {
                'message': f"'{args['locationId']}' already exists."
            }, 409
        else:
            # otherwise, we can add the new location record
            # create new dataframe containing new values
            new_data = pd.DataFrame({
                'locationId': [args['locationId']],
                'name': [args['name']],
                'rating': [args['rating']]
            })
            # add the newly provided values
            data = data.append(new_data, ignore_index=True)
            data.to_csv('locations.csv', index=False)  # save back to CSV
            return {'data': data.to_dict()}, 200  # return data with 200 OK
    
    def patch(self):
        parser = reqparse.RequestParser()  # initialize parser
        parser.add_argument('locationId', required=True, type=int)  # add args
        parser.add_argument('name', store_missing=False)  # name/rating are optional
        parser.add_argument('rating', store_missing=False)
        args = parser.parse_args()  # parse arguments to dictionary
        
        # read our CSV
        data = pd.read_csv('locations.csv')
        
        # check that the location exists
        if args['locationId'] in list(data['locationId']):
            # if it exists, we can update it, first we get user row
            user_data = data[data['locationId'] == args['locationId']]
            
            # if name has been provided, we update name
            if 'name' in args:
                user_data['name'] = args['name']
            # if rating has been provided, we update rating
            if 'rating' in args:
                user_data['rating'] = args['rating']
            
            # update data
            data[data['locationId'] == args['locationId']] = user_data
            # now save updated data
            data.to_csv('locations.csv', index=False)
            # return data and 200 OK
            return {'data': data.to_dict()}, 200
        
        else:
            # otherwise we return 404 not found
            return {
                'message': f"'{args['locationId']}' location does not exist."
            }, 404
    
    def delete(self):
        parser = reqparse.RequestParser()  # initialize parser
        parser.add_argument('locationId', required=True, type=int)  # add locationId arg
        args = parser.parse_args()  # parse arguments to dictionary

        # read our CSV
        data = pd.read_csv('locations.csv')
        
        # check that the locationId exists
        if args['locationId'] in list(data['locationId']):
            # if it exists, we delete it
            data = data[data['locationId'] != args['locationId']]
            # save the data
            data.to_csv('locations.csv', index=False)
            # return data and 200 OK
            return {'data': data.to_dict()}, 200
        
        else:
            # otherwise we return 404 not found
            return {
                'message': f"'{args['locationId']}' location does not exist."
            }


api.add_resource(Users, '/users')  # add endpoints
api.add_resource(Locations, '/locations')

if __name__ == '__main__':
    app.run()  # run our Flask app

@gadget1 ofcoarse if you replace the csv CRUD with MySql.
Why do you ask?

it does not work for all http methods

at line 36, if no index is given it may lead to ValueError: If using all scalar values, you must pass an index, so its better if we put something like index=[0].. else everything is too good for beginners!

Having issues when POST via POSTMAN. GET works fine
{
"message": "The browser (or proxy) sent a request that this server could not understand."
}
127.0.0.1 - - [20/Jan/2023 10:11:31] "POST /users?userId=abc123&name=The%20Rock&city=Los%20Angeles HTTP/1.1" 400 -

thoughts ?

In the docs: https://flask-restful.readthedocs.io/en/0.3.8/reqparse.html#basic-arguments it looks like reqparse will be deprecated. Also, there's another argument to add_argument "location="args" that will make sure the add_argument will check the URL string only. After I put in "location="args", parse_args worked. I don't have advice on the deprecation.

Having issues when POST via POSTMAN. GET works fine { "message": "The browser (or proxy) sent a request that this server could not understand." } 127.0.0.1 - - [20/Jan/2023 10:11:31] "POST /users?userId=abc123&name=The%20Rock&city=Los%20Angeles HTTP/1.1" 400 -

thoughts ?

You can lso use parser.add_argument('xxxx', required=True, location="json"). to read JSON values as well, if you instead don't want to have messy query string for every request. Although, if anyone is going to use this beyond a learning example, should probably use something other than reqparse to read the arguments since it will be deprecated.