Path: csiph.com!usenet.pasdenom.info!dedibox.gegeweb.org!gegeweb.eu!nntpfeed.proxad.net!proxad.net!feeder1-2.proxad.net!news.tele.dk!news.tele.dk!small.news.tele.dk!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
MIME-Version: 1.0
Sender: chris@rebertia.com
In-Reply-To: <52C9BF95.5000006@gkayaalp.com>
References: <52C9BF95.5000006@gkayaalp.com>
Date: Sun, 5 Jan 2014 14:09:14 -0800
Subject: Re: Postfix conditionals
From: Chris Rebert <clp2@rebertia.com>
To: =?UTF-8?B?R8O2a3R1xJ8gS2F5YWFscA==?= <self@gkayaalp.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Cc: Python <python-list@python.org>
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.4974.1388959764.18130.python-list@python.org>
Lines: 68
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:63230

On Sun, Jan 5, 2014 at 12:24 PM, G=C3=B6ktu=C4=9F Kayaalp <self@gkayaalp.co=
m> 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 t=
he
> 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 =3D 1) if True else (x =3D 2)
      File "<stdin>", line 1
        (x =3D 1) if True else (x =3D 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 o=
f
> 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