Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!newsfeed.xs4all.nl!newsfeed3.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.001 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'python,': 0.02; 'syntax': 0.04; 'postfix': 0.07; 'python:': 0.09; 'similar,': 0.09; 'statements': 0.09; 'violates': 0.09; '--------': 0.10; 'runs': 0.10; 'email addr:python.org>': 0.11; 'python': 0.11; 'jan': 0.12; 'posted': 0.15; '3):': 0.16; 'abusing': 0.16; 'added.': 0.16; 'benefit.': 0.16; 'chris,': 0.16; 'determines': 0.16; 'dislike': 0.16; 'notation,': 0.16; 'op.': 0.16; 'readability': 0.16; 'received:72.5': 0.16; 'received:72.5.230': 0.16; 'received:sender1.zohomail.com': 0.16; 'received:zohomail.com': 0.16; 'statement)': 0.16; 'syntaxerror:': 0.16; 'ternary': 0.16; 'email addr:python.org,': 0.16; 'language': 0.16; 'wrote:': 0.18; 'thoughts': 0.19; '>>>': 0.22; 'example': 0.22; 'this?': 0.23; 'header:User-Agent:1': 0.23; '>>>': 0.24; 'adds': 0.24; 'cheers,': 0.24; 'looks': 0.24; 'question': 0.24; 'cc:2**0': 0.24; 'cc:no real name:2**0': 0.24; '>': 0.26; 'equivalent': 0.26; 'mention': 0.26; 'second': 0.26; 'header:In-Reply-To:1': 0.27; 'function': 0.29; 'chris': 0.29; "doesn't": 0.30; 'compared': 0.30; 'statement': 0.30; "i'm": 0.30; '(which': 0.31; 'code': 0.31; 'posting': 0.31; '"",': 0.31; 'perl': 0.31; 'piece': 0.31; 'purely': 0.31; 'file': 0.32; 'another': 0.32; 'community': 0.33; '(i.e.': 0.33; 'actual': 0.34; 'date:': 0.34; 'knowledge': 0.35; 'there': 0.35; 'i.e.': 0.36; 'hi,': 0.36; 'two': 0.37; 'list': 0.37; 'list.': 0.37; 'to:addr:python-list': 0.38; 'list,': 0.38; 'pm,': 0.38; 'rather': 0.38; 'little': 0.38; 'subject:': 0.39; 'to:addr:python.org': 0.39; 'how': 0.40; 'break': 0.61; 'subject:Fwd': 0.61; 'skip:* 10': 0.61; 'from:charset:utf-8': 0.61; 'first': 0.61; 're:': 0.63; 'kind': 0.63; 'email name :python-list': 0.65; 'here': 0.66; 'reply': 0.66; 'believe': 0.68; 'invalid': 0.68; 'statement,': 0.68; 'superior': 0.69; 'opinions': 0.70; 'lack': 0.78; 'actually,': 0.84; 'rebert': 0.84; 'side- effects': 0.84; 'not:': 0.91; 'write:': 0.91 Date: Mon, 06 Jan 2014 00:12:17 +0200 From: =?UTF-8?B?R8O2a3R1xJ8gS2F5YWFscA==?= User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: python-list@python.org Subject: Fwd: Re: Postfix conditionals References: In-Reply-To: X-Forwarded-Message-Id: Content-Type: multipart/alternative; boundary="------------070602060602040108090007" X-ZohoMailClient: External X-Zoho-Virus-Status: 2 X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 207 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1388959945 news.xs4all.nl 2949 [2001:888:2000:d::a6]:51997 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:63231 This is a multi-part message in MIME format. --------------070602060602040108090007 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit This was sent to me as a private reply to a question that I have posted to python-list@python.org, so I am forwarding it to here. Chris, please send your messages to the list, and cc the OP. -------- Original Message -------- Subject: Re: Postfix conditionals Date: Sun, 5 Jan 2014 14:09:14 -0800 From: Chris Rebert To: Göktuğ Kayaalp CC: Python On Sun, Jan 5, 2014 at 12:24 PM, Göktuğ Kayaalp wrote: > Hi, > > AFAIK, we do not have "postfix conditionals" in Python, i.e. a condition > appended to a > statement, which determines whether the statement runs or not: > > py> for i in [False]: > ... break if not i > > The above piece of code is equivalent to this in Python: > > py> for i in [False]: > ... if not i > ... break > > I believe that the first example is superior to the second example when the > two is compared > for readability and intuitiveness. I'm going to have to disagree. I dislike how this obscures the if-statement, complicates the language grammar, and adds another unnecessary way to express the same thing (which violates TOOWTDI) with little countervailing benefit. > We already have a ternary statement that > looks similar, > > py> print('hi') if True else None Actually, to be pedantic, it's a ternary *expression*. Using it purely for side-effects (i.e. as a statement) is rather unidiomatic, in the same way that abusing list comprehensions, e.g.: [print(i) for i in range(42)] is frowned upon. Not to mention that the ternary doesn't work for actual statements (print() is just a function call in Python 3): >>> (x = 1) if True else (x = 2) File "", line 1 (x = 1) if True else (x = 2) ^ SyntaxError: invalid syntax > so I reckon there would be no breakage in old code if this kind of syntax > was added. Ruby has > this, and AFAIK Perl also does. > > I lack the knowledge of whether the community has opinions on this kind of > notation, so I am > posting this here instead of the ideas list. What are your thoughts on > this? You can already write: for i in [False]: if not i: break if you feel the need for terseness or a one-liner. Perhaps this satisfies your desire? Cheers, Chris --------------070602060602040108090007 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 8bit This was sent to me as a private reply to a question that I have posted
to python-list@python.org, so I am forwarding it to here.

Chris, please send your messages to the list, and cc the OP.

-------- Original Message --------
Subject: Re: Postfix conditionals
Date: Sun, 5 Jan 2014 14:09:14 -0800
From: Chris Rebert <clp2@rebertia.com>
To: Göktuğ Kayaalp <self@gkayaalp.com>
CC: Python <python-list@python.org> 


On Sun, Jan 5, 2014 at 12:24 PM, Göktuğ Kayaalp <self@gkayaalp.com> wrote:
> Hi,
>
> AFAIK, we do not have "postfix conditionals" in Python, i.e. a condition
> appended to a
> statement, which determines whether the statement runs or not:
>
>   py> for i in [False]:
>   ...     break if not i
>
> The above piece of code is equivalent to this in Python:
>
>   py> for i in [False]:
>   ...    if not i
>   ...        break
>
> I believe that the first example is superior to the second example when the
> two is compared
> for readability and intuitiveness.

I'm going to have to disagree. I dislike how this obscures the
if-statement, complicates the language grammar, and adds another
unnecessary way to express the same thing (which violates TOOWTDI)
with little countervailing benefit.

> We already have a ternary statement that
> looks similar,
>
>   py> print('hi') if True else None

Actually, to be pedantic, it's a ternary *expression*. Using it purely
for side-effects (i.e. as a statement) is rather unidiomatic, in the
same way that abusing list comprehensions, e.g.:

    [print(i) for i in range(42)]

is frowned upon.
Not to mention that the ternary doesn't work for actual statements
(print() is just a function call in Python 3):

    >>> (x = 1) if True else (x = 2)
      File "<stdin>", line 1
        (x = 1) if True else (x = 2)
           ^
    SyntaxError: invalid syntax

> so I reckon there would be no breakage in old code if this kind of syntax
> was added.  Ruby has
> this, and AFAIK Perl also does.
>
> I lack the knowledge of whether the community has opinions on this kind of
> notation, so I am
> posting this here instead of the ideas list.  What are your thoughts on
> this?

You can already write:

    for i in [False]:
        if not i: break

if you feel the need for terseness or a one-liner. Perhaps this
satisfies your desire?

Cheers,
Chris


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