Handling Errors Within Your Application

As with all code, eventually bugs and other exceptions will come up and risk ruining everything inside your app. Fortunately, Kyoukai handles these errors for you, and allows you to process them safely.

Error handlers are a way of handling errors easily. They are automatically called when an exception is encounted inside a route.

For example, if you have a piece of faulty code:

return "{}".format(a)  # 'a' is not defined

A NameError will normally be raised. However, Kyoukai will automatically catch the error, and re-raise it as a HTTP 500 exception. Normally, this exception wouldn’t be handled, and would respond to the client with a 500 body. However, it is possible to catch this exception and do what you wish with it.

The errorhandler decorator

To create an error handler, you simply wrap an existing function with the errorhandler decorator, providing the integer error code that you wish to handle. So for example, to create a 500 error handler, you would do:

async def handle_500(ctx: HTTPRequestContext, exc: HTTPException):
    return repr(exception_to_handle)

Of course, you can have anything in the body of the error handler. Whatever is returned from this error handler is sent back to the client.

New in version 2.2.1.

You can also have an error handler handle multiple codes in the same function by decorating it multiple times, or passing a range of errors to handle.

# handle error 502 and errors 400 (inclusive) to 414 (exclusive)
@app.root.errorhandler(400, 414)
async def handle_many(ctx: HTTPRequestContext, exc: HTTPException):

Changed in version 2.2.1.

If you need to access the arguments provided in the route when handling an error, you can use HTTPRequestContext.params, which will be a dict of the parameters passed to the function based on the routing URL.

HTTP Exceptions

HTTP exceptions in Kyoukai are handled by Werkzeug, which prevents having to rewrite large amounts of the error handling internally.

For more information on Werkzeug’s HTTPException, see werkzeug.exceptions.HTTPException.

To abort out of a function early, you can use werkzeug.exceptions.abort() to raise a HTTPException:

if something is bad: