Conditional iteration

[at]

By the way,

I think by approving

a = b if condition else c

used to avloind

if condition:
        a = b
else:
        a = c

which is dealing with same psychological problem, Guido also recognizes some
need...

Is it redundant according to your criteria, yes I would say:

a = {True: a, False: c}[condition]

or 

a = [c, a][condition]

would yield exactly the same even in one sentence....

Cheers,

@


at wrote:

> My comments below.
> 
> Kind regards,
> @
> 
> 
> Carl Banks wrote:
> 
>> at wrote:
>>> Well, all I can say that for me as a user it would make sense...
>> 
>> Which is, like, step one out of a hundred for getting a syntax change
>> into the language.
>> 
>>> Curiosity: in what sense is it redundant?
>> 
>> It creates syntactical support for two different ways to do something.
>> If your plan were adopted, then we'd have two different spellings for
>> the same thing:
>> 
>> for i in a:
>>     if i != 0:
>>         use(i)
>> 
>> for i in a if i != 0:
>>     use(i)
> 
> With the current Python syntax, I can create for every two lines of code a
> dozen alternative implementations:
> 
> # example 1
> a = {}
> a['b'] = 'c'
> 
> versus:
> a = {'b': 'c'}
> 
> 
> # example 2
> l = []
> for l in some_list:
>         if some_condition:
>                 l.append(l)
> 
> versus:
> l = []
> for x in some_list:
>         if some_condition:
>                 l = l + [x]
> 
> or:
> l = [x for x in some_list if some_condition]
> 
> (the beautiful one)
> 
> So your argument doesn't mean much I would say!
> 
>> 
>> Now, redundant syntax isn't a deal breaker by itself.  You have to ask
>> what is buys you.  In this case, all it does is save you a single level
>> of indentation--that's it.  There's no performance benefit.  It doesn't
>> simplify logic.  It doesn't make the code any more readable of clear.
>> It's only a minor improvement in conciseness.  It hardly saves any
>> typing (unless you indent by hand).  Even its one clear benefit, saving
>> indentation, is something you can already get with "if not x:
>> continue".
> 
> 
> Well there is a clear performance benefit, or more precisely a
> productivity benefit. And -please- do not underestimate this for a
> language like Python, which has many supporters due to its perceived and
> high productivity and challenged on this point by languages like Ruby.
> 
> 'for x in some_list if some_condition:'
> 
> is psychological very strong, because the brain will most likely treat the
> in the same way as :
> 
>         for every apple in the fruitbasket take one if green
> 
> 
> Basically upon reading this first line you know exactly to what list of
> items your next section of code applies.
> 
> But again everything is a matter of taste and I assume that's why the
> change control body is put into the hand of one person.
> 
> 
> 
>> Considering how little this syntax change buys, it really doesn't make
>> a lot of sense for a language that places high emphasis on avoiding
>> redundancy.
>> 
>> 
>>> All solution/workarounds I have seen so far involve creation of new
>>> lists (subsets) adding to more processing/computation/memory usage.
>>> Redundant suggests that you know alternatives that don't do that.
>>>
>>> Does Guido ever change his mind?
>> 
>> Yes, but I guarantee "it makes sense for me" isn't going to convince
>> him.  By the way, I'd suggest when posting to comp.lang.python and/or
>> python-list in the future, you put your replies beneath the quoted text
>> for the benefit of any future readers (not to mention present readers).
>>
> I hope this this thread will support the "it makes sense for me" with
> arguments. Again it is not my intention to fight windmills, but to see if
> there are strong arguments against it on one hand and if there supporters
> on the other hand.
> 
> 
>> 
>> Carl Banks