On Wed, 2013-07-10 at 19:49 -0400, Monty Taylor wrote: > I'd like top-post and hijack this thread for another exception related > thing: > > a) Anyone writing code such as: > > try: > blah() > except SomeException: > raise SomeOtherExceptionLeavingOutStackContextFromSomeException > > should be mocked ruthlessly.
Ok, mock me ruthlessly then. Part of designing any API is specifying what predictable exceptions it will raise. For any predictable error condition, you don't want callers to have to catch random exceptions from the underlying libraries you might be calling into. Say if I was designing an image downloading API, I'd do something like this: https://gist.github.com/markmc/5973868 Assume there's a tonne more stuff that the API would do. You don't want callers to have to catch socket.error exceptions and whatever other exceptions might be thrown. That works out as: Traceback (most recent call last): File "t.py", line 20, in <module> download_image('localhost', 3366, 'foobar') File "t.py", line 18, in download_image raise ImageDownloadFailure(host, port, path, e.strerror) __main__.ImageDownloadFailure: Failed to download foobar from localhost:3366: Connection refused Which is a pretty clear exception. But I think what you're saying is missing is the stack trace from the underlying exception. As I understood it, Python doesn't have a way of chaining exceptions like this but e.g. Java does. A little bit more poking right now shows up this: http://www.python.org/dev/peps/pep-3134/ i.e. we can't do the right thing until Python 3, where we'd do: def download_image(host, port, path): try: s = socket.create_connection((host, port)) except socket.error as e: raise ImageDownloadFailure(host, port, path, e.strerror) from e I haven't read the PEP in detail yet, though. Cheers, Mark. _______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
