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Re: Is vars() the most useless Python built-in ever?

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Manolo Martínez wrote:

> On 12/01/15 at 12:00pm, Steven D'Aprano wrote:
> > I'm trying to understand why vars() exists. Does anyone use it?
> 
> Well, I have this little podcast aggregator
> (https://github.com/manolomartinez/greg) that I and a bunch of other
> people use. I started writing it some years ago, and the code is a bit
> of a palimpsest, newer functionality reflecting my (somewhat) better
> understanding of the language. One of the oldest bits is this main()
> function:
> 
>         def main():  # parse the args and call whatever function was 
selected
>                 try:
>                         args = parser.parse_args(sys.argv[1:])
>                         args.func(vars(args))
>                 except AttributeError as err:
>                         if str(err) == "\'Namespace\' object has no 
attribute \'func\'":
>                                 parser.print_help()
>                         else:
>                                 print("Something has gone wrong: 
{}".format(err), file = sys.stderr, flush = True)
>          
> 
> To judge by this thread, this is probably wrong/noobish?

What probably is typical for a beginner in that snippet is that you don't 
trust the exception system and handle exceptions that will never occur once 
the script is debugged. Just write

args = parser.parse_args()
args.func(vars(args))

Now vars(). I see nothing wrong with it, but when I look into one of your 
func implementations

> def info(args):  # Provides information of a number of feeds
>     session = Session(args)
>     if "all" in args["names"]:
>         feeds = session.list_feeds()
>     else:
>         feeds = args["names"]
>     for feed in feeds:
>         pretty_print(session, feed)

I come to the conclusion that passing args directly could make your life 
easier:

def info(args):  
    """Provides information of a number of feeds"""
    session = Session(args)
    if "all" in args.names:
        feeds = session.list_feeds()
    else:
        feeds = args.names
    for feed in feeds:
        pretty_print(session, feed)

As far as I can see there is only one place where the key is not a constant, 
and you can rewrite that from 

>         try:
>             if args[value]:
>                 return args[value]
>         except KeyError:
>             pass

to

try:
    answer = getattr(args, value)
    if answer: 
        return answer
except AttributeError:
    pass

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Is vars() the most useless Python built-in ever? Steven D'Aprano <steve@pearwood.info> - 2015-12-01 12:00 +1100
  Re: Is vars() the most useless Python built-in ever? Josef Pktd <josef.pktd@gmail.com> - 2015-11-30 19:45 -0800
  Re: Is vars() the most useless Python built-in ever? Rick Johnson <rantingrickjohnson@gmail.com> - 2015-11-30 21:54 -0800
    Re: Is vars() the most useless Python built-in ever? Marko Rauhamaa <marko@pacujo.net> - 2015-12-01 09:34 +0200
      Re: Is vars() the most useless Python built-in ever? Rick Johnson <rantingrickjohnson@gmail.com> - 2015-12-11 13:06 -0800
    Re: Is vars() the most useless Python built-in ever? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-12-01 18:55 +1100
      Re: Is vars() the most useless Python built-in ever? Rick Johnson <rantingrickjohnson@gmail.com> - 2015-12-01 12:33 -0800
        Re: Is vars() the most useless Python built-in ever? Steven D'Aprano <steve@pearwood.info> - 2015-12-02 11:57 +1100
        Re: Is vars() the most useless Python built-in ever? Ian Kelly <ian.g.kelly@gmail.com> - 2015-12-01 22:48 -0600
          Re: Is vars() the most useless Python built-in ever? Rick Johnson <rantingrickjohnson@gmail.com> - 2015-12-11 14:13 -0800
            Re: Is vars() the most useless Python built-in ever? Steven D'Aprano <steve@pearwood.info> - 2015-12-12 15:44 +1100
              Re: Is vars() the most useless Python built-in ever? Chris Angelico <rosuav@gmail.com> - 2015-12-12 16:56 +1100
              Re: Is vars() the most useless Python built-in ever? Rick Johnson <rantingrickjohnson@gmail.com> - 2015-12-14 18:33 -0800
      Re: Is vars() the most useless Python built-in ever? Ben Finney <ben+python@benfinney.id.au> - 2015-12-02 12:47 +1100
    Re: Is vars() the most useless Python built-in ever? John Gordon <gordon@panix.com> - 2015-12-01 16:56 +0000
      Re: Is vars() the most useless Python built-in ever? Rick Johnson <rantingrickjohnson@gmail.com> - 2015-12-01 13:15 -0800
        Re: Is vars() the most useless Python built-in ever? "Albert Visser" <albert.visser@gmail.com> - 2015-12-02 19:08 +0100
    Re: Is vars() the most useless Python built-in ever? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-12-02 13:14 +1300
  Re: Is vars() the most useless Python built-in ever? eryk sun <eryksun@gmail.com> - 2015-12-01 01:22 -0600
    Re: Is vars() the most useless Python built-in ever? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-12-01 18:57 +1100
  Re: Is vars() the most useless Python built-in ever? Manolo Martínez <manolo@austrohungaro.com> - 2015-12-01 09:44 +0100
    Re: Is vars() the most useless Python built-in ever? Steven D'Aprano <steve@pearwood.info> - 2015-12-02 12:12 +1100
      Re: Is vars() the most useless Python built-in ever? Peter Otten <__peter__@web.de> - 2015-12-02 08:51 +0100
  Re: Is vars() the most useless Python built-in ever? Peter Otten <__peter__@web.de> - 2015-12-01 11:40 +0100
  Re: Is vars() the most useless Python built-in ever? Manolo Martínez <manolo@austrohungaro.com> - 2015-12-01 22:31 +0100
  Re: Is vars() the most useless Python built-in ever? Peter Otten <__peter__@web.de> - 2015-12-01 23:41 +0100
  Re: Is vars() the most useless Python built-in ever? boB Stepp <robertvstepp@gmail.com> - 2015-12-01 20:20 -0600
  Re: Is vars() the most useless Python built-in ever? wxjmfauth@gmail.com - 2015-12-01 23:46 -0800
  Re: Is vars() the most useless Python built-in ever? Serhiy Storchaka <storchaka@gmail.com> - 2015-12-02 10:22 +0200
  Re: Is vars() the most useless Python built-in ever? Manolo Martínez <manolo@austrohungaro.com> - 2015-12-02 10:09 +0100
  Re: Is vars() the most useless Python built-in ever? Chris Angelico <rosuav@gmail.com> - 2015-12-02 20:28 +1100
  Re: Is vars() the most useless Python built-in ever? Chris Angelico <rosuav@gmail.com> - 2015-12-02 20:33 +1100
  Re: Is vars() the most useless Python built-in ever? Manolo Martínez <manolo@austrohungaro.com> - 2015-12-02 10:40 +0100
  Re: Is vars() the most useless Python built-in ever? Peter Otten <__peter__@web.de> - 2015-12-02 11:48 +0100
  Re: Is vars() the most useless Python built-in ever? Chris Angelico <rosuav@gmail.com> - 2015-12-02 22:02 +1100
  Re: Is vars() the most useless Python built-in ever? eryk sun <eryksun@gmail.com> - 2015-12-02 05:34 -0600
  Re: Is vars() the most useless Python built-in ever? Serhiy Storchaka <storchaka@gmail.com> - 2015-12-04 10:42 +0200

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