Why Error is derived from EnvironmentError in shutil.py?

[Peng Yu]

On Thu, Nov 12, 2009 at 12:00 AM, alex23 <wuwei23 at gmail.com> wrote:
> On Nov 12, 2:46 pm, Peng Yu <pengyu... at 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?