Flask Error Handling

This is an error handling library for Flask Web applications.

• See: Flask Error Pages

• An error handler function returns a Flask response when some type of error is raised.
• An error handler must be registered with Flask.
  • The @app.errorhandler() decorator
  • The app.register_error_handler() method
• A handler can be registered for a status code, like 404, or an Exception subclass.

@app.errorhandler() decorator

@app.errorhandler(404)
def page_not_found(e):
    # note that we set the 404 status explicitly
    return render_template('404.html'), 404

app.register_error_handler() method

def page_not_found(e):
  return render_template('404.html'), 404

def create_app(config_filename):
    app = Flask(__name__)
    app.register_error_handler(404, page_not_found)
    return app

Flask_RESTPlus

The flask_restful.Api constructor also allows an errors dict to map Exception type names, message dict objects, and HTTP status.

• See Define Custom Error Messages

errors = {
    'ResourceDoesNotExist': {
        'message': "A resource with that ID no longer exists.",
        'status': 410,
        'extra': "Any extra information you want.",
    },
}

app = Flask(__name__)
api = flask_restful.Api(app, errors=errors)

Flask Error Handling Usage

This Flask Error Handling library extends the above rules. The bind_error_handlers call connects the Flask app object to the REGISTERED_EXC dictionary. Each HTTP status key has a list of Exception subclass types to register.

1. Add flask_error_handling package to the requirement.txt file.
2. Import the bind_error_handlers function from the package and call it.

Example

Create a REGISTERED_EXC dictionary and decide which exception to trap as HTTP status. AgeFormatError, UnderAgeError and ForbiddenRouteError are exceptions defined in the project.

from flask_error_handling.bindings import bind_error_handlers

REGISTERED_EXC = {
    400: [AgeFormatError, UnderAgeError],
    403: [ForbiddenRouteError],
}


bind_error_handlers(app, register_status_dict=REGISTERED_EXC)