Error Handling

Unified handling of exceptions and error pages improves maintainability and user experience.

Error Handlers:

from flask import render_template

@app.errorhandler(404)
def not_found(e):
    return render_template("404.html"), 404

@app.errorhandler(500)
def server_error(e):
    return render_template("500.html"), 500

Custom Exceptions:

class APIError(Exception):
    code = 400
    message = "Bad Request"

@app.errorhandler(APIError)
def handle_api_error(e):
    return {"error": e.message}, e.code

Blueprint-level Handling: Use register_error_handler on blueprint objects.

Logging Integration: Log serious errors, see Logging chapter.