[Python-Dev] Explicitly declaring expected exceptions for a block

[Paul Du Bois]

On 6/20/05, Dmitry Dvoinikov <dmitry at targeted.org> wrote:
> Excuse me if I couldn't find that in the existing PEPs, but
> wouldn't that be useful to have a construct that explicitly
> tells that we know an exception of specific type could happen
> within a block, like:

> ignore TypeError:
>     do stuff
> [else:
>     do other stuff]

If I understand PEP 343 correctly, it allows for easy implementation
of part of your request. It doesn't implement the else: clause, but
you don't give a use case for it either.

class ignored_exceptions(object):
   def __init__(self, *exceptions):
       self.exceptions = exceptions
   def __enter__(self):
       return None
   def __exit__(self, type, value, traceback):
       try:
           raise type, value, traceback
       except self.exceptions:
           pass

with ignored_exceptions(SomeError):
   do stuff

I don't see the use, but it's possible.

> The reason for that being self-tests with lots and lots of
> little code snippets like this:

If you're trying to write tests, perhaps a better use-case would be
something like:

with required_exception(SomeError):
   do something that should cause SomeError

paul