How to write this as a list comprehension?

[Piet van Oostrum]

"Rhodri James" <rhodri at wildebst.org.uk> writes:

> On Sat, 18 Jan 2014 16:00:45 -0000, Jussi Piitulainen
> <jpiitula at ling.helsinki.fi> wrote:

[...]

>> I would write that on three lines anyway, properly indented:
>>
>>   [ somefunc(mn,day,wd,name)
>>     for (then, name) in mylist
>>     let (_,mn,dy,_,_,_,wd,_,_) = localtime(then) ]
>>
>> It could be made to use existing keywords:
>>
>>   [ somefunc(mn,day,wd,name)
>>     for (then, name) in mylist
>>     with localtime(then) as (_,mn,dy,_,_,_,wd,_,_) ]
>
> Better, in that it's readable.  It's still storing up trouble, though.
>
> Seriously, what's inelegant about this?
>
> def meaningful_name(then, name):
>     _,mn,dy,_,_,_,wd,_,_ = localtime(then)
>     return somefunc(mn, dy, wd, name)
>
> ...
>
>     [meaningful_name(then, name) for (then, name) in mylist]
>
> I assume there's some good reason you didn't want somefunc() to do the
> localtime() itself?

Actually in my use case somefunc(mn,day,wd,name) was an expression, not
really a function call. I just presented it like that to make it a more
generalised abstract case. So in my case that would introduce an
additional function outside of the comprehension.

Let me summarize what my problem really was: In a comprehension you
generally need local name(s), which can only be introduced with the
'for' construction. But then the name(s) must be bound to an element of
a sequence/iterator. There is no way to bind the name(s) to a single
object other than putting that object in a one element sequence. I was
just looking for a way to avoid that. Functional programming languages
have a way to do this with the 'let' or 'where' construction which is
missing in Python.

Thanks everybody for your thoughts on this.
-- 
Piet van Oostrum <piet at vanoostrum.org>
WWW: http://pietvanoostrum.com/
PGP key: [8DAE142BE17999C4]