Flask.Exception.Chaining

app.py

"""
An example Flask app that uses Exceptions to return errors to clients
"""
from flask import Flask, jsonify

app = Flask(__name__)


class APIError(Exception):
    """All custom API Exceptions"""
    pass


class APIAuthError(APIError):
    """Custom Authentication Error Class."""
    code = 403
    description = "Authentication Error"


@app.errorhandler(APIError)
def handle_exception(err):
    """Return custom JSON when APIError or its children are raised"""
    response = {"error": err.description, "message": ""}
    if len(err.args) > 0:
        response["message"] = err.args[0]
    # Add some logging so that we can monitor different types of errors 
    app.logger.error(f"{err.description}: {response["message"]}")
    return jsonify(response), err.code

@app.errorhandler(500)
def handle_exception(err):
    """Return JSON instead of HTML for any other server error"""
    app.logger.error(f"Unknown Exception: {str(err)}")
    app.logger.debug(''.join(traceback.format_exception(etype=type(err), value=err, tb=err.__traceback__)))
    response = {"error": "Sorry, that error is on us, please contact support if this wasn't an accident"}
    return jsonify(response), 500


@app.route("/")
def hello():
    return jsonify("Hello World!"), 200


@app.route("/BadBoy")
def fail():
    raise Exception('Someone has been naughty')

                     
def check_user_exists(username):
  """ Some function that returns True if username is in the DB"""
  return True
             
                     
def check_password_is_correct(username, password):
  """ Some function that returns True if password for username is correct """
  return True

                     
@router.route("/user/login", methods=['POST'])
def user_login():
  if "email" not in request.data:
    raise APIAuthError('Missing email value')
  
  if "password" not in request.data:
    raise APIAuthError('Missing password value')
    
  if check_user_exists(request.data["email"]) and check_password_is_correct(request.data["email"], request.data["password"]):
    return "Success", 200
  else:
    raise APIAuthError('Incorrect Credentials')


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