Re: Set a flag on the function or a global?

Date	2015-06-17 09:51 +1000
From	Cameron Simpson <cs@zip.com.au>
Subject	Re: Set a flag on the function or a global?
References	<557fdbd6$0$11097$c3e8da3@news.astraweb.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.530.1434500492.13271.python-list@python.org> (permalink)

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On 16Jun2015 18:18, Steven D'Aprano <steve+comp.lang.python@pearwood.info> wrote:
>On Tuesday 16 June 2015 10:35, MRAB wrote:
>> On 2015-06-16 01:24, sohcahtoa82@gmail.com wrote:
>>> Using a keyword argument for the edir function is the most intuitive
>>> and easy to read, IMO.
>
>edir() has a keyword argument: edir(x, dunders=False) suppresses the return
>of dunder names. But since the primary purpose of [e]dir is, in my opinion,
>to be used interactively, needing to type an extra 15 characters to hide
>dunders is too inconvenient.

I'm just catching up here, but have now read the whole thread.

I am personally against a global (==> single variable affecting all callers) of 
any kind, be it a function attribute or whatever. Why? For that same reason 
that we discourage use of functions like os.chdir or os.umask except in rare 
circumstances: the single call inevitably affects the entire program behaviour.

Your intended use case may be interactive, where I agree the convenience looks 
nice. However, I think it inevitable that someone imports your edir function as 
an aid to writing friendly debugging messages is a larger program, and thus is 
escapes into noninteractive use. (As an example, I have a class named "O" which 
I use as a base class for many classes, especially in the debugging phase; its 
major semantic is friendlier __str__ and __repr__ for exactly the same reasons 
you wrote "edir", and with similar effect.)

On that basis (avoiding global state) my preference would be strongly to rely 
entirely on your keyword argument (dunder=False) and to offer two flavors, such 
as the "edir" and "edir_" suggested elsewhere. The user can always import 
"edir_ as edir_noisy" if they are of the mindset which dislikes single trailing 
underscores.

[...]
>> But it's meant to be used interactively. If they're using it in a
>> script, they'd most likely set the argument appropriately.
>
>Yes.

Ideally yes. "Most likely"? I have less confidence there.

>The primary use-case (at least *my* use-case, and hopefully others) is to
>have "from module import edir as dir" in their Python startup file. That
>means that when running interactively, they will get the enhanced version of
>dir, but when running a script or an application they'll just get the
>regular one.

This fits well with two functions, then they can import "edir" or "edir_" as 
dir as they see fit.

>Besides, apart from the inspect module, which probably shouldn't, who uses
>dir() programmatically?

Directly, perhaps rarely. But I use my O.__str__ method implicitly quite a lot, 
and it has a similar purpose to your edir. (It is not the same, so the parallel 
is not perfect.)

Cheers,
Cameron Simpson <cs@zip.com.au>

All who love Liberty are enemies of the State.  - Karl Hess

Thread

Set a flag on the function or a global? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-15 23:57 +0000
  Re: Set a flag on the function or a global? Chris Angelico <rosuav@gmail.com> - 2015-06-16 10:07 +1000
  Re: Set a flag on the function or a global? Ethan Furman <ethan@stoneleaf.us> - 2015-06-15 17:19 -0700
  Re: Set a flag on the function or a global? Ben Finney <ben+python@benfinney.id.au> - 2015-06-16 10:20 +1000
    Re: Set a flag on the function or a global? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-16 19:07 +1000
  Re: Set a flag on the function or a global? Ethan Furman <ethan@stoneleaf.us> - 2015-06-15 17:21 -0700
  Re: Set a flag on the function or a global? sohcahtoa82@gmail.com - 2015-06-15 17:24 -0700
    Re: Set a flag on the function or a global? MRAB <python@mrabarnett.plus.com> - 2015-06-16 01:35 +0100
      Re: Set a flag on the function or a global? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-16 18:18 +1000
        Re: Set a flag on the function or a global? Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-06-16 13:45 +0100
          Re: Set a flag on the function or a global? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-16 22:46 +0000
        Re: Set a flag on the function or a global? Cameron Simpson <cs@zip.com.au> - 2015-06-17 09:51 +1000
          Re: Set a flag on the function or a global? Steven D'Aprano <steve@pearwood.info> - 2015-06-18 00:59 +1000
            Re: Set a flag on the function or a global? Laura Creighton <lac@openend.se> - 2015-06-17 17:06 +0200
              Re: Set a flag on the function or a global? Steven D'Aprano <steve@pearwood.info> - 2015-06-18 01:55 +1000
                Documenting a function signature (was: Set a flag on the function or a global?) Ben Finney <ben+python@benfinney.id.au> - 2015-06-18 10:04 +1000
                Re: Documenting a function signature (was: Set a flag on the function or a global?) Ian Kelly <ian.g.kelly@gmail.com> - 2015-06-17 18:10 -0600
                Re: Documenting a function signature (was: Set a flag on the function or a global?) Chris Angelico <rosuav@gmail.com> - 2015-06-18 10:14 +1000
                Re: Documenting a function signature (was: Set a flag on the function or a global?) random832@fastmail.us - 2015-06-18 08:37 -0400
                Re: Documenting a function signature (was: Set a flag on the function or a global?) Laura Creighton <lac@openend.se> - 2015-06-18 23:38 +0200
                Re: Documenting a function signature Ben Finney <ben+python@benfinney.id.au> - 2015-06-19 10:41 +1000
  Re: Set a flag on the function or a global? Ron Adam <ron3200@gmail.com> - 2015-06-15 20:24 -0400
    Re: Set a flag on the function or a global? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-16 19:15 +1000
      Re: Set a flag on the function or a global? Ron Adam <ron3200@gmail.com> - 2015-06-16 07:02 -0400
  Re: Set a flag on the function or a global? Chris Angelico <rosuav@gmail.com> - 2015-06-16 10:32 +1000
  Re: Set a flag on the function or a global? Paul Rubin <no.email@nospam.invalid> - 2015-06-15 17:37 -0700
    Re: Set a flag on the function or a global? Ethan Furman <ethan@stoneleaf.us> - 2015-06-15 17:53 -0700
      Re: Set a flag on the function or a global? Paul Rubin <no.email@nospam.invalid> - 2015-06-15 19:04 -0700
    Re: Set a flag on the function or a global? MRAB <python@mrabarnett.plus.com> - 2015-06-16 02:15 +0100
    Re: Set a flag on the function or a global? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-16 18:30 +1000
  Re: Set a flag on the function or a global? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-16 07:06 +0100
    Re: Set a flag on the function or a global? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-16 19:28 +1000
  Re: Set a flag on the function or a global? Jonas Wielicki <jonas@wielicki.name> - 2015-06-16 12:00 +0200
  Re: Set a flag on the function or a global? Michael Torrie <torriem@gmail.com> - 2015-06-16 07:44 -0600
  Re: Set a flag on the function or a global? Michael Torrie <torriem@gmail.com> - 2015-06-16 07:56 -0600
  Re: Set a flag on the function or a global? Peter Otten <__peter__@web.de> - 2015-06-16 15:59 +0200
  Re: Set a flag on the function or a global? Ethan Furman <ethan@stoneleaf.us> - 2015-06-16 07:57 -0700

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