Example script of a PUT API method implemented with Flask

users_put.py

class Users(Resource):
    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
            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