[Python-Dev] cpython: Rename contextlib.ignored() to contextlib.ignore().

[Giampaolo Rodola']

On Fri, Oct 11, 2013 at 11:00 AM, Antoine Pitrou <solipsis at 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.
>
>
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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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