Fun with reverse sorts

[David Di Biase]

I did see that actually, I thought it was only applied to specifying default
parameters and wasn't sure if it ALSO applied to putting it into a function.
In a way however, I see what you're getting at - it's basically the same
thing you're just specifying a default value the same way...

Ok problem resolved.

Grazie tanto ;-)

David

On Fri, Oct 3, 2008 at 12:08 AM, Chris Rebert <clp at rebertia.com> wrote:

> On Thu, Oct 2, 2008 at 8:07 PM, David Di Biase <dave.dibiase at gmail.com>
> wrote:
> > Hi there,
> >
> > I'm sorting an expansive list descending according to a list of tuples.
> > Basically it has to sort the last value in the tuple (3) but if they are
> the
> > same then it should resort to using the second last value (2). Now
> according
> > to my very limited testing I've somewhat figured out that this SHOULD
> work:
> >
> > list.sort(lambda a, b: (cmp(a[3], b[3]), cmp(a[2], b[2])) [a[3] == b[3]],
> > reverse = True)
>
> Rather than defining a comparison function here (which is less
> efficient), you can use the 'key' argument, which specifies a function
> which is called for each item and returns a so-called key value that
> the corresponding element should be sorted according to. Also, so your
> slicing "[a[3] == b[3]]" isn't necessary because Python is smart and
> sorts tuples that way anyway. Finally, be careful not to use "list" as
> a variable name as this shadows the builtin 'list' type.
>
> So the improved code is:
>
> your_list.sort(key=lambda elem: (elem[3], elem[2]), reverse=True)
>
> >
> > Here's an example of the list: [(34,23,54,34), (34,23,230,34),
> > (34,23,523,334), (34,23,15,17), (34,23,54,17), (45,23,43,123),
> > (564,23,543,23), (23,54,600,23), (34,54,23,654), (43,54,32,34)]
> >
> > My first question is in regards to style first. The style guide for
> Python
> > doesn't seem to state this (if it has I missed it) but should I be doing
> > reverse=True or reverse = True with the spaces. lol this is so miniscule
> but
> > it's good to know. Also, does this function look/feel right to all the
> pros
> > out there. Is there a better way of doing it?
>
> Actually, this is mentioned in PEP 8. You might not be familiar with
> the term in use though ("keyword argument") which describes 'reverse'.
> Here's the relevant section:
>
> """
> - Don't use spaces around the '=' sign when used to indicate a
>      keyword argument or a default parameter value.
>
>      Yes:
>
>          def complex(real, imag=0.0):
>              return magic(r=real, i=imag)
>
>      No:
>
>          def complex(real, imag = 0.0):
>              return magic(r = real, i = imag)
> """
>
> So you want the former: reverse=True
>
> Cheers,
> Chris
> --
> Follow the path of the Iguana...
> http://rebertia.com
>
> >
> > I'm still wrapping my head around ways of accomplishing proper sorts!
> >
> > Dave
> >
> > --
> > http://mail.python.org/mailman/listinfo/python-list
> >
> >
>
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