On Thu, Nov 12, 2009 at 7:10 AM, Peng Yu <pengyu...@gmail.com> wrote: > On Thu, Nov 12, 2009 at 12:00 AM, alex23 <wuwe...@gmail.com> wrote: >> On Nov 12, 2:46 pm, Peng Yu <pengyu...@gmail.com> wrote: >>> I see Error is derived from EnvironmentError in shutil.py. >>> >>> class Error(EnvironmentError): >>> pass >>> >>> I'm wondering why EnvironmentError can not be raised directly. Why >>> Error is raised instead? >> >> This way you can explicitly trap on shutil.Error and not intercept any >> other EnvironmentError that might be raised. >> >> And as it's a descendent of EnvironmentError, it can still be caught >> by any handlers looking for such exceptions. > > It is true that an exception class is usually defined in a module and > all the exceptions raised in this module should be of this derived > class? Is it the general practice in python?
It is common, but not universal. Several of the modules in the stdlib use the technique. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
