[Python-Dev] arguments policy: **kwargs.pop()

[Guido van Rossum]

I'm not sure what you're worried about here. Modifying kwds doesn't
actually modify the dict that was passed in. So are you just talking about
the style issue? Or would you also object to this:

def foo(x=1):
    x += 1

?


On Thu, Apr 10, 2014 at 10:12 PM, Christian Tismer <tismer at stackless.com>wrote:

> Hi guys,
>
> I tried to find advice for hours, but failed so fer, so here is my
> question:
>
> Whenever I think to adopt a new module that does a good job, I always
> can't stand the temptation to look at the coding style and certain
> principles.
>
> Then I rather often see things like this:
>
> class someclass(object):
>     # note that there is no comment about argument destruction...
>
>     def __init__(self, **kwargs):
>         first_arg = kwargs.pop('option_1', somedefault)
>         ...
>         nth_arg = kwargs.pop('option_n', somedefault')
>         ...
>
> That is:
> There are arguments "consumed" rigorously by the __init__ of a class,
> although it would be equivalent to use kwargs.get(..., ...).
>
> Happened to me again, today and blocked me completely, since I don't
> know if I saw bad programming style or if I'm mislead.
>
> I agree there are valid cases when if makes sense to filter out some
> arguments
> that a subsequently called super() might not be able to handle.
> Bu even then, I would probably have a copy and make the filtering more
> explicit.
>
> But most of the time, there is no reason for using this pattern, and there
> is also no comment stating that the argument dict is modified by the callee
> for no good reason.
>
> I always used the policy that arguments are never changed by a function,
> unless explicitly stated.
> But since I see this pattern quite frequently, I wanted to ask if I am
> right by
> thinking this way, or if the general policy is more like "arguments may be
> destroyed by default".
>
> What do you think? Is this bad style and should be noticed somewhere,
> or is the caller supposed to protect the arguments, or are my worries
> useless?
>
> Thanks & cheers -- Chris
>
> --
> Christian Tismer             :^)   <mailto:tismer at stackless.com>
> Software Consulting          :     Have a break! Take a ride on Python's
> Karl-Liebknecht-Str. 121     :    *Starship* http://starship.python.net/
> 14482 Potsdam                :     PGP key -> http://pgp.uni-mainz.de
> phone +49 173 24 18 776  fax +49 (30) 700143-0023
> PGP 0x57F3BF04       9064 F4E1 D754 C2FF 1619  305B C09C 5A3B 57F3 BF04
>       whom do you want to sponsor today?   http://www.stackless.com/
>
> _______________________________________________
> Python-Dev mailing list
> Python-Dev at python.org
> https://mail.python.org/mailman/listinfo/python-dev
> Unsubscribe:
> https://mail.python.org/mailman/options/python-dev/guido%40python.org
>



-- 
--Guido van Rossum (python.org/~guido)
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-dev/attachments/20140410/afdb830c/attachment.html>