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Date: Fri, 30 Aug 2013 09:48:10 +0200
From: Antoon Pardon <antoon.pardon@rece.vub.ac.be>
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To: python-list@python.org
Subject: Re: semicolon at end of python's statements
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Op 30-08-13 09:25, Chris Angelico schreef:
> On Fri, Aug 30, 2013 at 5:15 PM, Antoon Pardon
> <antoon.pardon@rece.vub.ac.be> wrote:
>> Op 30-08-13 06:55, Ben Finney schreef:
>>> Ben Finney <ben+python@benfinney.id.au> writes:
>>>
>>>> Fábio Santos <fabiosantosart@gmail.com> writes:
>>>>
>>>>> It is a shame that this is not possible in python. for..if exists in
>>>>> comprehensions and not in regular loops but that would be nice
>>>>> sometimes.
>>>>     for foo in (spam for spam in sequence if predicate(spam)): …
>>>
>>> Better:
>>>
>>>     for foo in filter(predicate, sequence):
>>>         process(foo)
>>
>> Well better in what way? You now have to translate a predicate
>> expression into a predicate function. Which AFAIU was one of
>> the reasons to move away from map/filter to list comprehension.
>>
>> As I understand it, python made a move away from map and filter
>> towards list comprehension. Chris seems to want some of the
>> possibilities that came with that incorporated into the for
>> statement. And your suggestion is to go back to the old kind
>> of filter way.
> 
> No, actually Ben's quite right - assuming the predicate is a simple
> function,

But why should we assume that? Suppose I would like to process all
odd items in a list. A comprehension kind of notation would be

|  for item in lst if item % 2:
|      process items

Which we would have to turn into

|  for item in filter(lambda nr: nr % 2, lst):
|      process items

But AFAIR, one of the driving forces behind the introduction to list
comprehension, and thus a move away from map and filter was to get rid
of the lambda's in this kind of situations.

> of course (Python's lambda notation is a bit clunky for
> comparisons); as of Python 3, filter() is lazy and is pretty much what
> I'm doing here.

Lazy or not, is AFAICS, not a point here.

-- 
Antoon Pardon