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@gmail.com> wrote:

On 11 April 2013 23:52, Ram Rachum <ram.rachum@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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