Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Chris Angelico <rosuav@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Useless expressions [was Re: Undefined behaviour in C]
Date: Mon, 28 Mar 2016 12:38:19 +1100
Lines: 36
Message-ID: <mailman.99.1459129574.28225.python-list@python.org>
References: <mailman.8.1457732171.12893.python-list@python.org> <mailman.433.1458546438.12893.python-list@python.org> <56f02196$0$1588$c3e8da3$5496439d@news.astraweb.com> <mailman.29.1458713374.2244.python-list@python.org> <nctrak$rbh$1@dont-email.me> <mailman.45.1458730161.2244.python-list@python.org> <ncu691$4aq$1@dont-email.me> <mailman.78.1458789868.2244.python-list@python.org> <nd0oaa$rsb$1@dont-email.me> <56f42d9f$0$1618$c3e8da3$5496439d@news.astraweb.com> <nd1ggm$v4q$1@dont-email.me> <56f55e2e$0$1619$c3e8da3$5496439d@news.astraweb.com> <87wpoq1omm.fsf@elektro.pacujo.net> <56f5f81d$0$1585$c3e8da3$5496439d@news.astraweb.com> <87io0a6j1w.fsf@nightsong.com> <56f67ee3$0$1583$c3e8da3$5496439d@news.astraweb.com> <mailman.36.1458998575.28225.python-list@python.org> <nd651e$21g$1@dont-email.me> <mailman.37.1459002640.28225.python-list@python.org> <nd69eb$hqo$1@dont-email.me> <87poug5t0c.fsf@nightsong.com> <nd8g4p$aqk$1@dont-email.me> <56f887c1$0$1598$c3e8da3$5496439d@news.astraweb.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8
In-Reply-To: <56f887c1$0$1598$c3e8da3$5496439d@news.astraweb.com>
Precedence: list
Xref: csiph.com comp.lang.python:105891

On Mon, Mar 28, 2016 at 12:24 PM, Steven D'Aprano <steve@pearwood.info> wrote:
>>
>>    f()         # Probably OK
>>    g()         # Probably OK
>>    f()+g()     # Probably not OK
>
> You don't and can't know what's "probably not" okay unless you know what
> type of object both f and g return.
>
> Don't think about floats and ints and strings. Think of complex objects with
> operator overloading. You're probably thinking of `x + y`. Instead, think
> of things like:
>
> graph + node
> database + table
>
> in a procedural style instead of a functional style. With operator
> overloading, we have the ability to write domain-specific little languages.

I would still look askance at code that adds two things and drops the
result, though. The compiler can't discard it, but if a linter
complains, I'd support that. A DSL that requires you to do this is,
imo, poorly designed. It'll make every subsequent maintainer wonder if
the code is buggy or not.

But it's still...

> ... not the compiler's job to cast value judgements on what is good or
> likely style, it must accept anything legal. If you want something to make
> value judgements about style, or get warnings about what looks like legal
> code but might be an error, then you should use a linter like PyChecker,
> Pylint, Jedi or similar. That's not the compiler's job.

Exactly.

ChrisA