Path: csiph.com!newsfeed.hal-mli.net!feeder3.hal-mli.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!news.tele.dk!feed118.news.tele.dk!news.tele.dk!small.news.tele.dk!newsfeed.xs4all.nl!newsfeed1a.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
MIME-Version: 1.0
In-Reply-To: <53303b8a$0$29994$c3e8da3$5496439d@news.astraweb.com>
References: <9daf0806-02de-4447-964c-c8f8953c23e5@googlegroups.com> <10101874-2995-4acd-9851-989603f052e3@googlegroups.com> <bd158c7b-5511-472c-bce3-cc7b6b7747f6@googlegroups.com> <e2b2b9d5-56bd-4455-b8c3-205000d9acb3@googlegroups.com> <mailman.8369.1395437459.18130.python-list@python.org> <a0403642-c384-4623-bbfd-77c48285ec96@googlegroups.com> <mailman.8377.1395456097.18130.python-list@python.org> <dcd72881-7ee2-4bc3-90ab-7912b4bea05b@googlegroups.com> <lgj4sp$7ed$1@speranza.aioe.org> <532d5bd9$0$29994$c3e8da3$5496439d@news.astraweb.com> <lgoh7j$otg$1@speranza.aioe.org> <mailman.8440.1395651801.18130.python-list@python.org> <87bnwv2a5v.fsf@elektro.pacujo.net> <mailman.8446.1395661782.18130.python-list@python.org> <53303b8a$0$29994$c3e8da3$5496439d@news.astraweb.com>
Date: Tue, 25 Mar 2014 06:12:47 +1100
Subject: Re: Explanation of this Python language feature? [x for x in x for x in x] (to flatten a nested list)
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
Content-Type: text/plain; charset=UTF-8
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.8457.1395688376.18130.python-list@python.org>
Lines: 41
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:68893

On Tue, Mar 25, 2014 at 1:04 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
>> But which of these is truly more readable?
>>
>> squares = []
>> for n in range(30):
>>     squares.append(n * n)
>>
>> squares = [n * n for n in range(30)]
>
> Readable for whom?
>
> List comprehension syntax is often completely obscure to beginners. A
> beginner would say that the explicit for-loop is more readable.
>
> Actually, a *real* beginner, whose main programming experience before
> Python was Pascal, would probably even say that the first example was an
> unreadable mess. What's range(30)? What's this ".append" business? What
> does [] mean? I know this because I was this beginner, once. The first
> few times I tried reading Python code, I couldn't make head or tail of
> it. "for" I recognised, because it was the same keyword as Pascal and
> Hypertalk use. Pretty much everything else might as well have been
> Bulgarian.

Actually, that's a very good point. Python's for loop is more often
called a foreach loop in other languages, and Python completely lacks
any concept of a "classic" iteration-over-integer for loop. That is a
point of confusion. However, that's going to come up on both branches,
so it's not really a mark against either.

Incidentally, I've often modified my loop counter, in C or REXX or any
other language. About the only situation where I actually miss it in
Python, though, is iterating over a list and mutating the list on the
way through; and even that can often be done in other ways (maybe a
list comp, filtering out some of the elements?). It's amazing how
something can be so utterly fundamental (I mean, come ON! Who can
imagine a language with no equivalent of the basic "do i=1 to 10"
(REXX) or "for (int i=0;i<10;++i)" (C++) loop???) and yet so
dispensable.

ChrisA