6_exceptions.md

Handling exceptions

There may be cases where you may want to respond with a custom response instead of a 500 Internal Server Error when an exception(s) is raised. Or you might want to override the default 404 handler. Enter exception handlers.

# examples/6_exceptions/exceptions.py
from japronto import Application, RouteNotFoundException


# Those are our custom exceptions we want to turn into 200 response.
class KittyError(Exception):
    def __init__(self):
        self.greet = 'meow'


class DoggieError(Exception):
    def __init__(self):
        self.greet = 'woof'


# The two handlers below raise exceptions which will be turned
# into 200 responses by the handlers registered later
def cat(request):
    raise KittyError()


def dog(request):
    raise DoggieError()


# This handler raises ZeroDivisionError which doesnt have an error
# handler registered so it will result in 500 Internal Server Error
def unhandled(request):
    1 / 0


app = Application()

r = app.router
r.add_route('/cat', cat)
r.add_route('/dog', dog)
r.add_route('/unhandled', unhandled)


# These two are handlers for `Kitty` and `DoggyError`s.
def handle_cat(request, exception):
    return request.Response(text='Just a kitty, ' + exception.greet)


def handle_dog(request, exception):
    return request.Response(text='Just a doggie, ' + exception.greet)


# You can also override default 404 handler if you want
def handle_not_found(request, exception):
    return request.Response(code=404, text="Are you lost, pal?")


# register all the error handlers so they are actually effective
app.add_error_handler(KittyError, handle_cat)
app.add_error_handler(DoggieError, handle_dog)
app.add_error_handler(RouteNotFoundException, handle_not_found)

app.run()

The source code for all the examples can be found in examples directory.

Next: Extending request