from flask import Flask
from flask_restful import Api

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

api.add_resource(ContactList, "/contacts")


if __name__ == '__main__':
    from object_SQLAlchemy import db
    db.init_app(app)
    app.run(port=5000)


class Contact(Resource):
    parser = reqparse.RequestParser()
    parser.add_argument(
        'contact_no',
        type=str,
        required=True,
        help="This field cannot be left blank"
    )

    @throttling.Throttle("10/m", strategy=2)
    def get(self, name):
        contact = Contacts.findbyname(name)
        if contact:
            return contact.json()
        return {"message": "Contact does not exist."}, 404

from ..app_alchemy import api, app


@api.errorhandler(Exception)
def handle_error(e):
    return {"error": str(e)}


@app.errorhandler(500)
def handle_error_app(e):
    return {"error": str(e.args[0])}


@app.handle_exception(Exception)
def handle_it_app(e):
    return {"error": str(e.args[0])}


@api.handle_exception(Exception)
def handle_it(e):
   return {"error": str(e.args[0])}

{"message": "Internal Server Error"}