On Fri, Oct 11, 2013 at 11:00 AM, Antoine Pitrou <solip...@pitrou.net>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. > > Regards > > Antoine. > > > _______________________________________________ > 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/g.rodola%40gmail.com > I'm with Antoine here. Despite "with ignore(OSError): os.remove" looks appealing to the eye I think many people will end up thinking it's fine to write long "ignore" blocks, because that's perfectly fine when using the "with" statement. Point is this is actually a "try" block disguised as a "with", and "try" blocks should usually be followed by very few indented lines (usually just 1) for a very good reason. -1 --- Giampaolo https://code.google.com/p/pyftpdlib/ https://code.google.com/p/psutil/ https://code.google.com/p/pysendfile/
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