On 10/11/2013 5:00 AM, Antoine Pitrou wrote: > > Let me answer here to Nick's argument on the tracker (made last year, > before the patch was committed): > >> As with many context managers, a key benefit here is in the priming >> effect for readers. In this code: >> >> try: >> # Whatever >> except (A, B, C): >> pass >> >> the reader doesn't know that (A, B, C) exceptions will be ignored >> until the end. The with statement form makes it clear before you >> start reading the code that certain exceptions won't propagate: >> >> with ignored(A, B, C): >> # Whatever > > The problem with this argument is that it assumes a very specific idiom: > i.e. writing long "try" blocks in the purpose of silencing exceptions. > > I'd like to make the following points: > > - when catching an exception, the common (and recommended) behaviour is > to do something else - not merely silencing it. Silencing is not very > common in my experience, except in badly written code > > - when catching an exception, it is recommended for the "try" block to > be as slim as possible - so that you don't catch other unintended > exceptions by mistake. This is a point I already made in PEP 3151. > Many exception classes (OSError, KeyError, RuntimeError...) are > polysemic. > > The bottom line is that there shouldn't be any long "try" blocks > followed by a single "except FooException: pass" clause in well-written > code. The presence of such an idiom is a strong code smell. > > Therefore contextlib.ignore() seems aimed at making it easier to write > bad code, not good code. I don't think it should exist in the stdlib.
In case anyone wants to look at the original issue, it's http://bugs.python.org/issue15806 And Antoine has again taught me a new word: polysemic: having more than one meaning; having multiple meanings -- Eric. _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
