Path: csiph.com!news.swapon.de!fu-berlin.de!uni-berlin.de!not-for-mail
From: Chris Angelico <rosuav@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Pylint prefers list comprehension over filter...
Date: Fri, 6 May 2016 12:55:05 +1000
Lines: 24
Message-ID: <mailman.425.1462503307.32212.python-list@python.org>
References: <572BF2BF.6000000@icloud.com> <1462498631.232041.599637409.25D91C08@webmail.messagingengine.com> <mailman.422.1462498634.32212.python-list@python.org> <ngh0hu$4og$1@dont-email.me> <CAPTjJmqJmkTp85wWZm_GF1gRKSRv5UE7Ck4jZM2NBSwAnFKk-Q@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8
In-Reply-To: <ngh0hu$4og$1@dont-email.me>
Precedence: list
Xref: csiph.com comp.lang.python:108211

On Fri, May 6, 2016 at 12:46 PM, Dan Sommers <dan@tombstonezero.net> wrote:
> filter used to build a list, but now it doesn't (where "used to" means
> Python 2.7 and "now" means Python 3.5; I'm too lazy to track down the
> exact point(s) at which it changed):
>
>     Python 2.7.11+ (default, Apr 17 2016, 14:00:29)
>     [GCC 5.3.1 20160409] on linux2
>     Type "help", "copyright", "credits" or "license" for more information.
>     >>> filter(lambda x:x+1, [1, 2, 3, 4])
>     [1, 2, 3, 4]
>
>     Python 3.5.1+ (default, Apr 17 2016, 16:14:06)
>     [GCC 5.3.1 20160409] on linux
>     Type "help", "copyright", "credits" or "license" for more information.
>     >>> filter(lambda x:x+1, [1, 2, 3, 4])
>     <filter object at 0x7f26a9ef3320>

Most of these kinds of changes happened in 3.0, where
backward-incompatible changes were accepted. A whole bunch of things
stopped returning lists and started returning lazy iterables - range,
filter/map, dict.keys(), etc - because most of the time, they're
iterated over once and then dropped.

ChrisA