Most efficient way to "pre-grow" a list?

[Steven D'Aprano]

On Fri, 06 Nov 2009 18:46:33 -0800, gil_johnson wrote:

> I don't have the code with me, but for huge arrays, I have used
> something like:
> 
>>>> arr[0] = initializer
>>>> for i in range N:
>>>>      arr.extend(arr)
> 
> This doubles the array every time through the loop, and you can add the
> powers of 2 to get the desired result. Gil

Why is it better to grow the list piecemeal instead of just allocating a 
list the size you want in one go?

arr = [x]*size_wanted



-- 
Steven