[Python-ideas] Allow key='attribute_name' to various sorting functions

[Haoyi Li]

A more generic and useful thing would be kind of what scala/groovy have:
shorthands for defining function literals:

Groovy:
myList.sort{it.startTime}

Scala:
myList.sort(_.startTime)

Where "_.startTime" and "it.startTime" are shorthand for "x => x.startTime"
or python's "lambda x: x.startTime". You could probably get something
similar in python:

sorted(entries, key = x.datetime_created)

if you did some magic with x to make looking up an attribute return a
lambda that returns that attribute of its argument.

-Haoyi



On Thu, Apr 11, 2013 at 7:05 PM, Oscar Benjamin
<oscar.j.benjamin at gmail.com>wrote:

> On 11 April 2013 23:52, Ram Rachum <ram.rachum at gmail.com> wrote:
> > On Friday, April 12, 2013 1:35:20 AM UTC+3, Carl Meyer wrote:
> >>
> >> On 04/11/2013 04:24 PM, Ram Rachum wrote:
> >> > I often want to sort objects by an attribute. It's cumbersome to do
> >> > this:
> >> >
> >> >     sorted(entries, key=lambda entry: entry.datetime_created)
> >> >
> >> > Why not allow this instead:
> >> >
> >> >     sorted(entries, key='datetime_created')
> >>
> >>     from operator import attrgetter
> >>     sorted(entries, key=attrgetter('datetime_created'))
> >>
> >> You can alias attrgetter to an even shorter name if you like.
> >
> > That's still cumbersome in my opinion.
>
> I don't think it's that cumbersome. Leaving aside the import line
> you're only having to specify two things for your key function: that
> it's an attribute (attrgetter) and the name of the attribute
> ('datetime_created'). It's not possible for this to be any more
> succinct without using special case implicit rules which are generally
> a bad thing. I like the fact that the API for the sorted function is
> so simple I can remember all of its arguments and exactly what they do
> without ever needing to look it up.
>
>
> Oscar
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