Registered error handler in Python/Flask application does not work-CodePudding

I create a Python/Flask application with the following code in main.py:

import json

from flask import Flask, jsonify
from werkzeug.exceptions import HTTPException, default_exceptions

from blueprints import test

def create_app(config_filename=None) -> Flask:
   """Application factory function
   """
   app = Flask(__name__, instance_relative_config=True)
   if config_filename:
       app.config.from_pyfile(config_filename)

   for exc in default_exceptions:
       app.register_error_handler(exc, handle_error)        

   register_blueprints(app)
   return app

def handle_error(error):
   code = 500
   if isinstance(error, HTTPException):
       code = error.code
   return jsonify(error='error', code=code)    


def register_blueprints(app: Flask):
   """Register blueprints
   """
   app.register_blueprint(test.bp)


def handle_exception(ex: HTTPException):
   """Return JSON instead of HTML for HTTP errors."""
   # start with the correct headers and status code from the error
   response = ex.get_response()
   # replace the body with JSON
   response.data = json.dumps({
       "code": ex.code,
       "error": ex.name,
       "message": ex.description,
   })
   response.content_type = "application/json"
   return response


if __name__ == '__main__':
   main_app = create_app()
   main_app.run(host='0.0.0.0', port=80, debug=True, threaded=False)

and the source code of the test.py blueprint is:

from flask import Blueprint, jsonify, request
from werkzeug.exceptions import HTTPException, default_exceptions

bp = Blueprint('blabla', __name__)

@bp.route('/blabla', methods=['POST'])
def blabla():
   """Test blueprint
   """
   raise MyException()

class MyException(HTTPException):

   code = 409
   name = 'My Exception'
   description = 'My Exception'

unfortunately when i execute the endpoint, the exception is not handled by the method, defined in the main.py

I even decided and tried to register error handlers in the blueprint, but the result is the same - the exception is not handled by the methods.

Here is the modified test.py

from flask import Blueprint, jsonify, request
from werkzeug.exceptions import HTTPException, default_exceptions

bp = Blueprint('blabla', __name__)

@bp.errorhandler(409)
def error_handler(e):
    return handle_error(e)

@bp.route('/blabla', methods=['POST'])
def blabla():
    """Test blueprint
    """
    raise MyException()

def handle_error(error):
    code = 500
    if isinstance(error, HTTPException):
        code = error.code
    return jsonify(error='error', code=code)

class MyException(HTTPException):

    code = 409
    name = 'My Exception'
    description = 'My Exception'

Can someone tell me what is my error? Why the exception is not handled by the error methods?

CodePudding user response：

This example is directly from flask, which has slight differences in terms of your code, for example, in @app.errorhandler(404) decorator they check request users as follows request.path.startswith(''), maybe this is not the source of your error but I recommend that you carefully read the examples and instructions to handle errors using blue print error handlers.

from flask import jsonify, render_template

# at the application level
# not the blueprint level
@app.errorhandler(404)
def page_not_found(e):
    # if a request is in our blog URL space
    if request.path.startswith('/blog/'):
        # we return a custom blog 404 page
        return render_template("blog/404.html"), 404
    else:
        # otherwise we return our generic site-wide 404 page
        return render_template("404.html"), 404

@app.errorhandler(405)
def method_not_allowed(e):
    # if a request has the wrong method to our API
    if request.path.startswith('/api/'):
        # we return a json saying so
        return jsonify(message="Method Not Allowed"), 405
    else:
        # otherwise we return a generic site-wide 405 page
        return render_template("405.html"), 405

CodePudding user response：

Actually it came out, that the error handler has to be registered after the blueprints:

def register_blueprints(app: Flask):
    app.register_blueprint(test.bp)
    
    app.register_error_handler(HTTPException, handle_exception)

def handle_exception(ex: HTTPException):
    """Return JSON instead of HTML for HTTP errors."""
    # start with the correct headers and status code from the error
    response = ex.get_response()
    # replace the body with JSON
    response.data = json.dumps({
        "code": ex.code,
        "error": ex.name,
        "message": ex.description,
    })
    response.content_type = "application/json"
    return response