Bottle middleware to catch exceptions of a certain type?

Question

Given this simple Bottle code:

def bar(i):
    if i%2 == 0:
        return i
    raise MyError

@route('/foo')
def foo():
    try:
        return bar()
    except MyError as e:
        response.status_code = e.pop('status_code')
        return e

How would one write Bottle middleware so the same exception handling is done implicitly, so that code like this can work identically to above:

@route('/foo')
def foo():
    return bar()

Could you simply not derive your exception from bottle.HTTPResponse with the exception type then doing the appropriate thing to start with or is the source of your exception not part of your web application and therefore not already dependent on bottle? — Graham Dumpleton, Jan 24 '14 at 05:40
The exception is being thrown from an independent library; Bottle is only one frontend to it. — stackoverflowuser95, Jan 24 '14 at 05:46
Would a [Bottle plugin](http://bottlepy.org/docs/dev/plugindev.html) suffice? — ron rothman, Mar 03 '14 at 17:52

micimize · Accepted Answer · 2019-05-26T22:17:29.103

9

You can do this elegantly with a plugin leveraging abort:

from bottle import abort

def error_translation(func):
    def wrapper(*args,**kwargs):
        try:
            func(*args,**kwargs)
        except ValueError as e:
            abort(400, e.message)
    return wrapper

app.install(error_translation)

edited May 26 '19 at 22:17

answered Sep 24 '15 at 14:41

micimize

904
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16

What is the `abort()`? - does it mean `os.abort()`? – Val K May 25 '19 at 20:06
@ValK Just edited to add more context - it's a function provided by `bottle` for aborting a request with a code + message – micimize May 26 '19 at 22:18
Thank you for the clarification. – Val K May 28 '19 at 19:20

score 4 · Answer 2 · answered Jan 24 '14 at 08:45

Bottle respect the wsgi spec. You can use a classic wsgi middleware

from bottle import route, default_app, run, request

# push an application in the AppStack
default_app.push()


@route('/foo')
def foo():
    raise KeyError()


# error view
@route('/error')
def error():
    return 'Sorry an error occured %(myapp.error)r' % request.environ


# get the bottle application. can be a Bottle() instance too
app = default_app.pop()
app.catchall = False


def error_catcher(environ, start_response):
    # maybe better to fake the start_response callable but this work
    try:
        return app.wsgi(environ, start_response)
    except Exception as e:
        # redirect to the error view if an exception is raised
        environ['PATH_INFO'] = '/error'
        environ['myapp.error'] = e
        return app.wsgi(environ, start_response)


# serve the middleware instead of the applicatio
run(app=error_catcher)

Thanks, but is there a way I can show the error output (as JSON) and set the status code; without a redirect? - I'm thinking maybe a lambda in the `error_catcher` block... — stackoverflowuser95, Jan 26 '14 at 07:20
It's an internal redirect. And the error view can return some json. error_catcher is a wsgi application so you can do what you want/need. Read more about wsgi application: http://webpython.codepoint.net/wsgi_application_interface — gawel, Jan 29 '14 at 10:33
So how do I do it without a separate function? - E.g.: a lambda approach? — stackoverflowuser95, Feb 04 '14 at 09:37

Aminah Nuraini · Answer 3 · 2016-02-04T23:17:22.397

1

You can use this instead:

from bottle import error, run, route

@error(500)
def error_handler_500(error):
    return json.dumps({"status": "error", "message": str(error.exception)})

@route("/")
def index():
    a = {}
    a['aaa']

run()

edited Feb 04 '16 at 23:17

answered Feb 04 '16 at 22:56

Aminah Nuraini

18,120
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Bottle middleware to catch exceptions of a certain type?

3 Answers3