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Re: How to write this as a list comprehension?

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John Allsup <pydev@allsup.co> writes:

> Hi,
>
> I'd agree with the advice that it's not the best idea: readability sucks
> here, but consider the following:
>
>
> import time
>
> def somefunc(a,b,c,d): # dummy function
>     return "{} - {} - {} : {}".format(a,b,c,d)
> l = [(time.time(),"name {}".format(n)) for n in range(100)] # dummy data
>
> # the line in question
> labels = [somefunc(*(lambda t,n:
> (t.tm_mon,t.tm_mday,t.tm_wday,n))(time.localtime(x[0]),x[1])) for x in
> l]
>
>
> print(labels) # just to see the result
>
>
> If you find that hard to decipher, the consider the maintainability of
> code you write that uses such comprehensions.  You need to include
> comments that explain what this does, and it is easier to write a
> longhand version using .append() and variable assignments.  I presume
> performance won't be an issue determining the right approach, since then
> you'd be using C or C++.

I'll stay with

labels = [somefunc(mn, day, wd, name) 
            for then, name in mylist
            for _, mn, dy, _, _, _, wd, _, _ in [localtime(then)]]

where (sic!) the last part means as much as 
           where _, mn, dy, _, _, _, wd, _, _ = localtime(then)

I find the list comprehension preferable because it makes it more clear
that a new list is constructed from an existing list, something that is
not as immediately clear with the append construction.
-- 
Piet van Oostrum <piet@vanoostrum.org>
WWW: http://pietvanoostrum.com/
PGP key: [8DAE142BE17999C4]

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Thread

How to write this as a list comprehension? Piet van Oostrum <piet@vanoostrum.org> - 2014-01-18 00:19 +0100
  Re: How to write this as a list comprehension? Dan Stromberg <drsalists@gmail.com> - 2014-01-17 15:49 -0800
  Re: How to write this as a list comprehension? Rustom Mody <rustompmody@gmail.com> - 2014-01-17 19:25 -0800
    Re: How to write this as a list comprehension? Piet van Oostrum <piet@vanoostrum.org> - 2014-01-18 11:00 +0100
  Re: How to write this as a list comprehension? Peter Otten <__peter__@web.de> - 2014-01-18 09:36 +0100
    Re: How to write this as a list comprehension? Rustom Mody <rustompmody@gmail.com> - 2014-01-18 07:20 -0800
      Re: How to write this as a list comprehension? Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2014-01-18 18:00 +0200
        Re: How to write this as a list comprehension? "Rhodri James" <rhodri@wildebst.org.uk> - 2014-01-19 23:41 +0000
          Re: How to write this as a list comprehension? Piet van Oostrum <piet@vanoostrum.org> - 2014-01-20 12:02 +0100
            Re: How to write this as a list comprehension? Rustom Mody <rustompmody@gmail.com> - 2014-01-20 03:47 -0800
  Re: How to write this as a list comprehension? matej@ceplovi.cz (Matěj Cepl) - 2014-01-18 11:57 +0100
  Re: How to write this as a list comprehension? Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2014-01-18 12:53 +0100
    Re: How to write this as a list comprehension? Piet van Oostrum <piet@vanoostrum.org> - 2014-01-18 18:40 +0100
  Re: How to write this as a list comprehension? John Allsup <pydev@allsup.co> - 2014-01-19 01:24 +0000
    Re: How to write this as a list comprehension? Piet van Oostrum <piet@vanoostrum.org> - 2014-01-19 23:06 +0100

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