Flask custom error page 500 not working

Question

I have the following code in __init__.py

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

@app.errorhandler(500)
def internal_server_error(e):
    return render_template('500.html'), 500

@app.errorhandler(403)
def page_forbidden(e):
    return render_template('403.html'), 500

It used to catch all 500 errors and show my nice 500.html template. However I moved all my views into separate blueprint files and now the 500 errorhandler does not work. It is only that handler though. 404 works just fine.

If the server throws a 500 error, it will display the default Chrome INTERNAL SERVER ERROR message and not my template. Did I do something wrong when I created all my blueprints that would create this issue?

Here is the entire __init__.py file

import datetime
import mysql.connector
import os
from flask import Flask, render_template, session, request, Blueprint
from flask.ext.moment import Moment
from flask.ext.login import LoginManager
from db_classes import User

from info import info_blueprint
from claims import claims_blueprint
from users import users_blueprint
from members import members_blueprint
from drug import drug_blueprint
from auth import auth_blueprint
from formulary import formulary_blueprint

from config import MYSQL_USR, MYSQL_HOST, MYSQL_PASS, MYSQL_DB, MYSQL_PORT, second_to_live

from decorators import role_required

app = Flask(__name__, template_folder="static/templates")
app.config.from_object('config')

moment = Moment(app)

login_manager = LoginManager()
login_manager.init_app(app)
login_manager.session_protection = 'strong'
login_manager.login_view = 'login'

@login_manager.user_loader
def load_user(user_id):
    return User.query.get(int(user_id))


####################
#   Blueprints
####################

app.register_blueprint(info_blueprint)
app.register_blueprint(claims_blueprint)
app.register_blueprint(users_blueprint)
app.register_blueprint(members_blueprint)
app.register_blueprint(drug_blueprint)
app.register_blueprint(formulary_blueprint)
app.register_blueprint(auth_blueprint)



#####################
#   Error Routes
#####################  


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

@app.errorhandler(500)
def internal_server_error(e):
    return render_template('500.html'), 500

@app.errorhandler(403)
def page_forbidden(e):
    return render_template('403.html'), 500

#####################
#   Context Processors
#####################

@app.before_request
def make_session_permanent():
    session.permanent = True
    app.permanent_session_lifetime = datetime.timedelta(seconds=second_to_live)

@app.context_processor
def inject_time():
    return dict(current_time=datetime.datetime.utcnow())

if __name__ == "__main__":
    app.run(host= '0.0.0.0', debug=True)

Answer 1

Something I didn't realize... from the Flask docs

Please note that if you add an error handler for “500 Internal Server Error”, Flask will not trigger it if it’s running in Debug mode.