X-Received: by 10.129.27.3 with SMTP id b3mr27036591ywb.0.1458645821649; Tue, 22 Mar 2016 04:23:41 -0700 (PDT)
X-Received: by 10.50.83.34 with SMTP id n2mr307242igy.2.1458645821590; Tue, 22 Mar 2016 04:23:41 -0700 (PDT)
Path: csiph.com!usenet.blueworldhosting.com!feeder01.blueworldhosting.com!peer03.iad.highwinds-media.com!news.highwinds-media.com!feed-me.highwinds-media.com!y89no8575907qge.0!news-out.google.com!pn7ni16534igb.0!nntp.google.com!av4no1670723igc.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail
Newsgroups: comp.lang.python
Date: Tue, 22 Mar 2016 04:23:40 -0700 (PDT)
In-Reply-To: <ncr8n3$625$1@dont-email.me>
Complaints-To: groups-abuse@google.com
Injection-Info: glegroupsg2000goo.googlegroups.com; posting-host=24.63.27.64; posting-account=Jod8CwoAAAD06WqLVFnlf8nIDonFoRWK
NNTP-Posting-Host: 24.63.27.64
References: <mailman.8.1457732171.12893.python-list@python.org> <nbvqg5$3cm$1@dont-email.me> <mailman.23.1457749230.12893.python-list@python.org> <56e44258$0$1598$c3e8da3$5496439d@news.astraweb.com> <mailman.46.1457819135.12893.python-list@python.org> <8737rvxs89.fsf@elektro.pacujo.net> <nc2a7s$6dv$1@dont-email.me> <mailman.48.1457831488.12893.python-list@python.org> <nc4ffn$f6s$1@dont-email.me> <56e7483d$0$1608$c3e8da3$5496439d@news.astraweb.com> <nc7kjr$jj8$1@dont-email.me> <ncnhp9$tt7$1@dont-email.me> <ncnip4$1pb$1@ger.gmane.org> <CAPTjJmqA4rs74JWXinvqHhELzjhhe3MtAruS_WnDB7OG_=FbVA@mail.gmail.com> <mailman.423.1458525784.12893.python-list@python.org> <ncpin0$4m9$1@dont-email.me> <56f09973$0$1601$c3e8da3$5496439d@news.astraweb.com> <ncr8n3$625$1@dont-email.me>
User-Agent: G2/1.0
MIME-Version: 1.0
Message-ID: <f8a1d9ee-ee86-4355-bae7-4cfc5f6cebbd@googlegroups.com>
Subject: Re: The Cost of Dynamism (was Re: Pyhon 2.x or 3.x, which is faster?)
From: Ned Batchelder <ned@nedbatchelder.com>
Injection-Date: Tue, 22 Mar 2016 11:23:41 +0000
Content-Type: text/plain; charset=ISO-8859-1
X-Received-Bytes: 3680
X-Received-Body-CRC: 293645853
Xref: csiph.com comp.lang.python:105463

On Tuesday, March 22, 2016 at 7:05:20 AM UTC-4, BartC wrote:
> On 22/03/2016 01:01, Steven D'Aprano wrote:
> > Pythonic code probably uses a lot of iterables:
> >
> > for value in something:
> >      ...
> 
> > in preference to Pascal code written in Python:
> >
> > for index in range(len(something)):
> >      value = something[index]
> 
> (Suppose you need both the value and its index in the loop? Then the 
> one-line for above won't work. For example, 'something' is [10,20,30] 
> and you want to print:
> 
>   0: 10
>   1: 20
>   2: 30 )

Then you use enumerate:

    for index, value in enumerate(something):
        print("{}: {}".format(index, value))

Python has a number of iteration features that you don't find in other
languages.  You might find this introduction to them helpful:

Loop Like a Native: http://nedbatchelder.com/text/iter.html

> 
> >      ...
> > or worse:
> >
> > index = 0
> > while index < len(something):
> >      value = something[index]
> >      ...
> >      index += 1
> 
> > (I don't know where that while-loop idiom comes from. C? Assembly? Penitent
> > monks living in hair shirts in the desert and flogging themselves with
> > chains every single night to mortify the accursed flesh? But I'm seeing it
> > a lot in code written by beginners. I presume somebody, or some book, is
> > teaching it to them. "Learn Python The Hard Way" perhaps?)
> 
> Are you suggesting 'while' is not needed? Not everything fits into a 
> for-loop you know!

Steven wasn't saying 'while' is not needed. He was wondering about the
idiom of manually maintaining an integer count of the number of times
around a while loop ("I don't know where *that* while-loop idiom comes from").

While-loops are still useful in Python, but for-loops are much more common.

--Ned.