Catching a 500 server error in Flask

I love Flask's error catching. It's beautifully simple:

@app.errorhandler(404)
def pageNotFound(error):
    return "page not found"

works like charm. But it doesn't work for the 500 error code. I want to catch Python errors when something goes wrong an exception is raised in the code. Is that possible?

I should note that if I explicitly call return abort(500) in a view then the 500 errorhandler does work. So this is explicitly for when the Python code fails.

Is this possible?

Solution 1:

What you have described is, by default, how Flask works. My assumption is that you are running in debug mode, and therefore exceptions are being shown to you in the debug screen. Make sure debug mode is off, then try again. Here is a comment directly from the code itself:

Default exception handling that kicks in when an exception occurs that is not caught. In debug mode the exception will be re-raised immediately, otherwise it is logged and the handler for a 500 internal server error is used. If no such handler exists, a default 500 internal server error message is displayed.

Solution 2:

It works fine in my side:

from flask import Flask ,url_for,render_template,request,abort
from  werkzeug.debug import get_current_traceback
app = Flask(__name__)

@app.route('/')
def index():
    try:
        raise Exception("Can't connect to database")
    except Exception,e:
        track= get_current_traceback(skip=1, show_hidden_frames=True,
            ignore_system_exceptions=False)
        track.log()
        abort(500)
    return "index"

@app.errorhandler(500)
def internal_error(error):

    return "500 error"

@app.errorhandler(404)
def not_found(error):
    return "404 error",404

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

Flask will not set the error code for you, so make sure to also provide the HTTP status code when returning a response.

Solution 3:

here is my code snippt

@app.route('/')
def index():
    raise Exception("Can't connect to database")


@app.errorhandler(Exception)
def exception_handler(error):
    return "!!!!"  + repr(error)

Solution 4:

My solution to this was to turn on the propagation of exceptions, by modifying the config dictionary:

app = Flask(__name__)
...
app.config['PROPAGATE_EXCEPTIONS'] = True

Look at this other related question: Flask app raises a 500 error with no exception