[Python-ideas] Question about `list.insert`

[Antoine Pitrou]

On Fri, 07 Feb 2014 20:05:41 +0900
"Stephen J. Turnbull" <stephen at xemacs.org>
wrote:
> 
>  > Is there a good reason why `list.insert(whatever, 0)` doesn't
>  > opportunistically try to allocate more space at the left side of
>  > the list, so as to save the expensive operation of moving all 
>  > the items? I'm not saying it should reserve space there, just check if
>  > that space is available, and if so use it.
> 
> The problem is that it would have to have unholy carnal knowledge of
> OS internals (eg, of malloc).  First off, availability itself is
> non-portable, depending on a lot of things (eg, placement of malloc
> metadata and Python object metadata).

??? I don't understand what you're talking about.

It is perfectly possible while being portable. The proof is that
bytearray has a limited variant of that optimization (not for
insertions, but for deletions at the front).

Regards

Antoine.