Conditional iteration

[at]

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