[Python-ideas] More power in list comprehensions with the 'as' keyword

[Bruce Leban]

[t for t in [t.strip() for t in text.split('\n')] if t != '']


On Wed, Aug 27, 2008 at 10:00 AM, Imri Goldberg <lorgandon at gmail.com> wrote:

> +1 from me, I find myself doing that all the time as well.
>
> On Wed, Aug 27, 2008 at 7:51 PM, Tarek Ziadé <ziade.tarek at gmail.com>wrote:
>
>> Hello
>>
>> There's a pattern I am doing all the time: filtering out some elements of
>> a list, and cleaning them in the same move.
>>
>> For example, if I have a multi line text, where I want to:
>>
>> - keep non empty lines
>> - clean non empty lines
>>
>> I am doing:
>>
>>     >>> text = """
>>     ... this is a multi-line text\t
>>     ...
>>     ... \t\twith
>>     ...
>>     ... muliple lines."""
>>
>>     >>> [l.strip() for l in text.split('\n') if l.strip() != '']
>>     ['this is a multi-line text', 'with', 'muliple lines.']
>>
>> It is not optimal, because I call strip() twice. I could use ifilter then
>> imap or even use a real loop, but I
>> want my simple, concise, list comprehension !  And I couldn't find a
>> simple way to express it.
>>
>> The pattern can be generically resumed like this :
>>
>>    [transform(e) for e in seq if some_test(transform(e))]
>>
>> So what about using the 'as' keyword to extend lists comprehensions, and
>> to avoid calling transform() twice ?
>>
>> Could be:
>>
>>    [transform(e) as transformed for e in seq if some_test(transformed)]
>>
>> In my use case I would simply have to write;:
>>
>>   [l.strip() as stripped for l in text.split('\n') if stripped != '']
>>
>> Which seems to me clear and concise.
>>
>> Regards,
>> Tarek
>>
>> --
>> Tarek Ziadé | Association AfPy | www.afpy.org
>> Blog FR | http://programmation-python.org
>> Blog EN | http://tarekziade.wordpress.com/
>>
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>>
>
>
> --
> Imri Goldberg
> --------------------------------------
> www.algorithm.co.il/blogs/
> www.imri.co.il
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