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

Tue Dec 1 05:40:15 EST 2015

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