On Thursday, April 14, 2016 at 1:48:40 PM UTC-7, Michael Selik wrote:
> On Thu, Apr 14, 2016, 7:37 PM justin walters <walters.justi...@gmail.com>
> wrote:
>
> > On Apr 14, 2016 9:41 AM, "Martin A. Brown" <mar...@linux-ip.net> wrote:
> > >
> > >
> > > Greetings Justin,
> > >
> > > > score = sum_of_votes/num_of_votes
> > >
> > > >votes = [(72, 4), (96, 3), (48, 2), (53, 1), (26, 4), (31, 3), (68, 2),
> > (91, 1)]
> > >
> > > >Specifically, I'm wondering if this is a good algorithm for
> > > >weighted voting. Essentially a vote is weighted by the number of
> > > >votes it counts as. I realize that this is an extremely simple
> > > >algorithm, but I was wondering if anyone had suggestions on how to
> > > >improve it.
> > >
> > > I snipped most of your code. I don't see anything wrong with your
> > > overall approach. I will make one suggestion: watch out for
> > > DivisionByZero.
> > >
> > > try:
> > > score = sum_of_votes / num_of_votes
> > > except ZeroDivisionError:
> > > score = float('nan')
> > >
> > > In your example data, all of the weights were integers, which means
> > > that a simple mean function would work, as well, if you expanded the
> > > votes to an alternate representation:
> > >
> > > votes = [72, 72, 72, 72, 96, 96, 96, 48, 48, 53, 26, 26, 26, 26,
> > > 31, 31, 31, 68, 68, 91]
> > >
> > > But, don't bother!
> > >
> > > Your function can handle votes that have a float weight:
> > >
> > > >>> weight([(4, 1.3), (1, 1),])
> > > 2.695652173913044
> > >
> > > Have fun!
> > >
> > > -Martin
> > >
> > > --
> > > Martin A. Brown
> > > http://linux-ip.net/
> >
> > Thanks Martin!
> >
> > I'll add the check for division by zero. Didn't think about that. I think
> > I'm going to sanitize input anyways, but always better to be safe than
> > sorry.
> >
>
> I suggest not worrying about sanitizing inputs. If someone provides bad
> data, Python will do the right thing: stop the program and print an
> explanation of what went wrong, often a more helpful message than one you'd
> write. Use error handling mostly for when you want to do something *other*
> than stop the program.
>
> I'm not sure I'd use NaN instead of raise division by zero error. NaNs can
> be troublesome for downstream code that might not notice until it gets
> confusing. A div-by-zero error is clear and easier to track down because of
> the traceback.
>
> What do you think of using list comprehensions?
>
> weighted_sum = sum(rating * weight for rating, weight in votes)
> total_weights = sum(weight for rating, weight in votes)
> score = weighted_sum / total_weights
>
> It's two loops as I wrote it, which is instinctively slower, but it might
> actually execute faster because of the built-in sum vs a regular for loop.
> Not sure.
>
> >
I disagree with your notion of not sanitizing inputs.
If I'm the only person that will be using my program, then sure, I won't
sanitize inputs. It was my mistake and I should read the traceback and know
what I did wrong.
But if ANY third party is going to be using it, especially as part of a web
service of some kind, I'd much rather sanitize the inputs and tell the user
they did something bad than to have the script crash and give a 500 Internal
Server Error to the user.
Even worse, I definitely wouldn't want to give any hints of the source code
organization by letting the user see the traceback. I'll log it privately so I
can view it myself, of course.
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