sanic/docs/sanic/exceptions.md

Exceptions

Exceptions can be thrown from within request handlers and will automatically be handled by Sanic. Exceptions take a message as their first argument, and can also take a status code to be passed back in the HTTP response.

Throwing an exception

To throw an exception, simply raise the relevant exception from the sanic.exceptions module.

from sanic.exceptions import ServerError

@app.route('/killme')
async def i_am_ready_to_die(request):
	raise ServerError("Something bad happened", status_code=500)

You can also use the abort function with the appropriate status code:

from sanic.exceptions import abort
from sanic.response import text

@app.route('/youshallnotpass')
async def no_no(request):
        abort(401)
        # this won't happen
        text("OK")

Handling exceptions

To override Sanic's default handling of an exception, the @app.exception decorator is used. The decorator expects a list of exceptions to handle as arguments. You can pass SanicException to catch them all! The decorated exception handler function must take a Request and Exception object as arguments.

from sanic.response import text
from sanic.exceptions import NotFound

@app.exception(NotFound)
async def ignore_404s(request, exception):
	return text("Yep, I totally found the page: {}".format(request.url))

You can also add an exception handler as such:

from sanic import Sanic

async def server_error_handler(request, exception):
	return text("Oops, server error", status=500)

app = Sanic()
app.error_handler.add(Exception, server_error_handler)

In some cases, you might want to add some more error handling functionality to what is provided by default. In that case, you can subclass Sanic's default error handler as such:

from sanic import Sanic
from sanic.handlers import ErrorHandler

class CustomErrorHandler(ErrorHandler):
	def default(self, request, exception):
		''' handles errors that have no error handlers assigned '''
		# You custom error handling logic...
		return super().default(request, exception)
		
app = Sanic()
app.error_handler = CustomErrorHandler()

Useful exceptions

Some of the most useful exceptions are presented below:

• NotFound: called when a suitable route for the request isn't found.
• ServerError: called when something goes wrong inside the server. This usually occurs if there is an exception raised in user code.

See the sanic.exceptions module for the full list of exceptions to throw.