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

Giampaolo Rodola' g.rodola at gmail.com
Fri Oct 11 19:14:42 CEST 2013

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.

Python-Dev mailing list Python-Dev at 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/ -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20131011/b003a0e9/attachment.html>

More information about the Python-Dev mailing list