list comprehension return a list and sum over in loop

[KK Sasa]

Mark Lawrence於 2014年12月12日星期五UTC+8下午3時17分43秒寫道：
> On 12/12/2014 06:22, KK Sasa wrote:
> > Hi there,
> >
> > The list comprehension is results = [d2(t[k]) for k in xrange(1000)], where d2 is a function returning a list, say [x1,x2,x3,x4] for one example. So "results" is a list consisting of 1000 lists, each of length four. Here, what I want to get is the sum of 1000 lists, and then the result is a list of length four. Is there any efficient way to do this? Because I found it is slow in my case. I tried sum(d2(t[k]) for k in xrange(1000)), but it returned error: TypeError: unsupported operand type(s) for +: 'int' and 'list'. Thanks.
> >
> 
> I think you need something like this 
> http://stackoverflow.com/questions/19339/a-transpose-unzip-function-in-python-inverse-of-zip
> 
> I'll let you add the finishing touches if I'm correct :)
> 
> -- 
> My fellow Pythonistas, ask not what our language can do for you, ask
> what you can do for our language.
> 
> Mark Lawrence

Hi Mark and Yotam,
  Thanks for kind reply. I think I didn't make my problem clear enough. The slow part is "[d2(t[k]) for k in xrange(1000)]". In addition, I don't need to construct a list of 1000 lists inside, but my aim is to get the sum of all "d2(t[k])". I wonder if there is any method to sum up efficiently.