How to catch all exceptions with CherryPy?

cherrypy, exception, python

Solution

Docs somehow seem to miss this section. This is what I found while looking for detailed explanation for custom error handling from the source code.

Custom Error Handling

Anticipated HTTP responses

The 'error_page' config namespace can be used to provide custom HTML output for expected responses (like 404 Not Found). Supply a filename from which the output will be read. The contents will be interpolated with the values %(status)s, %(message)s, %(traceback)s, and %(version)s using plain old Python string formatting.

_cp_config = {
    'error_page.404': os.path.join(localDir, "static/index.html")
}

Beginning in version 3.1, you may also provide a function or other callable as an error_page entry. It will be passed the same status, message, traceback and version arguments that are interpolated into templates

def error_page_402(status, message, traceback, version):
    return "Error %s - Well, I'm very sorry but you haven't paid!" % status
cherrypy.config.update({'error_page.402': error_page_402})

Also in 3.1, in addition to the numbered error codes, you may also supply `error_page.default` to handle all codes which do not have their own error_page entry.

Unanticipated errors

CherryPy also has a generic error handling mechanism: whenever an unanticipated error occurs in your code, it will call `Request.error_response` to set the response status, headers, and body. By default, this is the same output as `HTTPError(500)`. If you want to provide some other behavior, you generally replace "request.error_response".

Here is some sample code that shows how to display a custom error message and send an e-mail containing the error

from cherrypy import _cperror

def handle_error():
    cherrypy.response.status = 500
    cherrypy.response.body = [
        "<html><body>Sorry, an error occurred</body></html>"
    ]
    sendMail('error@domain.com',
             'Error in your web app',
             _cperror.format_exc())

@cherrypy.config(**{'request.error_response': handle_error})
class Root:
    pass

Note that you have to explicitly set `response.body` and not simply return an error message as a result.

Problem

I use CherryPy to run a very simple web server. It is intended to process the `GET` parameters and, if they are correct, do something with them. ``` import cherrypy class MainServer(object): def index(self, **params): # do things with correct parameters if 'a' in params: print params['a'] index.exposed = True cherrypy.quickstart(MainServer()) ``` For example, ``` http://127.0.0.1:8080/abcde: 404 Not Found The path '/abcde' was not found. Traceback (most recent call last): File "C:\Python27\lib\site-packages\cherrypy\_cprequest.py", line 656, in respond response.body = self.handler() File "C:\Python27\lib\site-packages\cherrypy\lib\encoding.py", line 188, in __call__ self.body = self.oldhandler(*args, **kwargs) File "C:\Python27\lib\site-packages\cherrypy\_cperror.py", line 386, in __call__ raise self NotFound: (404, "The path '/abcde' was not found.") Powered by CherryPy 3.2.4 ``` I am trying to catch this exception and show a blank page because the clients do not care about it. Specifically, the result would be an empty body, no matter the url or query string that resulted in an exception. I had a look at documentation on error handling `cherrypy._cperror`, but I did not find a way to actually use it. Note: I gave up using `CherryPy` and found a simple solution using `BaseHTTPServer` (see my answer below)

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