slice notation as values?

[Bengt Richter]

On 10 Dec 2005 12:07:12 -0800, "Devan L" <devlai at gmail.com> wrote:

>
>Antoon Pardon wrote:
>> On 2005-12-10, Duncan Booth <duncan.booth at invalid.invalid> wrote:
>[snip]
>> >> I also think that other functions could benefit. For instance suppose
>> >> you want to iterate over every second element in a list. Sure you
>> >> can use an extended slice or use some kind of while. But why not
>> >> extend enumerate to include an optional slice parameter, so you could
>> >> do it as follows:
>> >>
>> >>   for el in enumerate(lst,::2)
>> >
>> > 'Why not'? Because it makes for a more complicated interface for something
>> > you can already do quite easily.
>>
>> Do you think so? This IMO should provide (0,lst[0]), (2,lst[2]),
>> (4,lst[4]) ...
>>
>> I haven't found a way to do this easily. Except for something like:
>>
>> start = 0:
>> while start < len(lst):
>>   yield start, lst[start]
>>   start += 2
>>
>> But if you accept this, then there was no need for enumerate in the
>> first place. So eager to learn something new, how do you do this
>> quite easily?
>
>>>> lst = ['ham','eggs','bacon','spam','foo','bar','baz']
>>>> list(enumerate(lst))[::2]
>[(0, 'ham'), (2, 'bacon'), (4, 'foo'), (6, 'baz')]
>
>No changes to the language necessary.
>
Or, without creating the full list intermediately,

 >>> lst = ['ham','eggs','bacon','spam','foo','bar','baz']
 >>> import itertools
 >>> list(itertools.islice(enumerate(lst), 0, None, 2))
 [(0, 'ham'), (2, 'bacon'), (4, 'foo'), (6, 'baz')]

Regards,
Bengt Richter