Example – Disabling traceback pages

If processing a request fails, by default Klein (and Twisted) show an error page that prints the traceback and other useful debugging information.

This is not desirable when you deploy code publicly, in such a case, you should disable this behaviour.

There are multiple ways to do this, you can do this on a Klein-app scope or change the default for the python process.

We will use following Klein app:

from klein import Klein

app = Klein()

def requestOK(self, request):
    return 'OK'

def requestKO(self, request):
    raise RuntimeError('Oops')

Example - Disable traceback pages on a single Klein app

This works by passing the displayTracebacks argument as False to app.run.

if __name__ == '__main__':
    import sys
    displayTracebacks = '--production' not in sys.args

    # The Klein app will not display tracebacks if the script is called
    # with a --production argument, but it will otherwise.
    app.run('localhost', 8080, displayTracebacks=displayTracebacks)

Example - Disable traceback pages process wide

This method also affects other Twisted Sites.

Under the hood, Klein uses twisted.web.server.Site, which has an instance variable displayTracebacks that defaults to True.

For the rationale behind that, check https://twistedmatrix.com/trac/ticket/135

# Disable tracebacks by default for any Site object.
from twisted.web.server import Site
Site.displayTracebacks = False

if __name__ == '__main__':
    # The Klein app won't display tracebacks
    app.run('localhost', 8080)