On Sat, Feb 20, 2010 at 10:48 PM, Steven D'Aprano
wrote:
> On Sat, 20 Feb 2010 21:21:47 -0800, Jonathan Gardner wrote:
>> For ten items, though, is it really faster to muck around with array
>> lengths than just copying the data over? Array copies are extremely fast
>> on modern processors.
>
> My
On Sun, 21 Feb 2010 11:07:24 -0800, marwie wrote:
>> x = SomeReallyBigListOrString
>> for item in x[1:]:
>> process(item)
>>
>> has to copy the entire list or string (less the first item). But
>> honestly, I've never found a situation where it actually mattered.
>
> Good grief, it copies that
On Feb 20, 5:55 pm, marwie wrote:
> On 21 Feb., 02:30, Steven D'Aprano
> cybersource.com.au> wrote:
> > Python lists are arrays of pointers to objects, so copying a slice is
> > fast: it doesn't have to copy the objects, just pointers. Deleting from
> > the end of the list is also quick, because
MRAB wrote:
Steven D'Aprano wrote:
[snip]
I'm sympathetic to your concern: I've often felt offended that doing
something like this:
x = SomeReallyBigListOrString
for item in x[1:]:
process(item)
has to copy the entire list or string (less the first item). But
honestly, I've never found a
On 21 Feb., 07:38, Carl Banks wrote:
> Numpy arrays can share underlying data like that when you take
> slices. For instance, this probably works the way you want:
>
> a = numpy.array([1,2,3,4,5,6])
> b = a[:3]
> c = a[3:]
>
> None of the actual data was copied here.
Hmm, that might be worth loo
On 21 Feb., 04:40, Steven D'Aprano wrote:
>
> Additionally, Python lists are over-allocated so that appends are fast. A
> list of (say) 1000 items might be over-allocated to (say) 1024 items, so
> that you can do 24 appends before the array is full and the array needs
> to be resized. This means t
On Sat, 20 Feb 2010 21:21:47 -0800, Jonathan Gardner wrote:
> On Sat, Feb 20, 2010 at 5:41 PM, Steven D'Aprano
> wrote:
>>
>> What the OP wants is:
>>
>> (1) assign the name l2 to l1[:10] without copying (2) resize l1 in
>> place to the first 10 items without affecting l2.
>>
>>
> For ten items,
On Feb 20, 4:55 pm, marwie wrote:
> Hello,
>
> I recently read about augmented assignments and that (with l1, l2
> being lists)
>
> l1.extend(l2)
>
> is more efficient than
>
> l1 = l1 + l2
>
> because unnecessary copy operations can be avoided. Now my question is
> if there's a similar th
On Sat, Feb 20, 2010 at 5:41 PM, Steven D'Aprano
wrote:
>
> What the OP wants is:
>
> (1) assign the name l2 to l1[:10] without copying
> (2) resize l1 in place to the first 10 items without affecting l2.
>
For ten items, though, is it really faster to muck around with array
lengths than just cop
Steven D'Aprano wrote:
[snip]
I'm sympathetic to your concern: I've often felt offended that doing
something like this:
x = SomeReallyBigListOrString
for item in x[1:]:
process(item)
has to copy the entire list or string (less the first item). But
honestly, I've never found a situation wh
On Sat, Feb 20, 2010 at 6:55 PM, marwie wrote:
> Now my question is
> if there's a similar thing for breaking a list into two parts. Let's
> say I want to remove from l1 everything from and including position 10
> and store it in l2. Then I can write
>
>l2 = l1[10:]
>del l1[10:]
With Py
On Sat, 20 Feb 2010 17:55:18 -0800, marwie wrote:
> On 21 Feb., 02:30, Steven D'Aprano cybersource.com.au> wrote:
>> Python lists are arrays of pointers to objects, so copying a slice is
>> fast: it doesn't have to copy the objects, just pointers. Deleting from
>> the end of the list is also quic
On 21 Feb., 02:41, Steven D'Aprano wrote:
> What the OP is doing is quite different:
>
> (1) copy l1[:10]
> (2) assign the name l2 to it
> (3) resize l1 in place to the first 10 items.
>
> What the OP wants is:
>
> (1) assign the name l2 to l1[:10] without copying
> (2) resize l1 in place to the f
On 21 Feb., 02:30, Steven D'Aprano wrote:
> Python lists are arrays of pointers to objects, so copying a slice is
> fast: it doesn't have to copy the objects, just pointers. Deleting from
> the end of the list is also quick, because you don't have to move memory,
> just clear some pointers and cha
On Sat, 20 Feb 2010 17:06:36 -0800, Jonathan Gardner wrote:
> On Sat, Feb 20, 2010 at 4:55 PM, marwie wrote:
[...]
>> l2 = l1[10:]
>> del l1[10:]
>>
>> But since I'm assigning a slice the elements will be copied. Basically,
>> I'm looking for something like l1.pop(10,len(l1)) which returns
On Sat, 20 Feb 2010 16:55:10 -0800, marwie wrote:
> Hello,
>
> I recently read about augmented assignments and that (with l1, l2 being
> lists)
>
> l1.extend(l2)
>
> is more efficient than
>
> l1 = l1 + l2
>
> because unnecessary copy operations can be avoided. Now my question is
> if
You can always implement your own data-structures or simply a function if
you need so. A language consist of building blocks and not buildings.
On Sun, Feb 21, 2010 at 6:36 AM, Jonathan Gardner <
jgard...@jonathangardner.net> wrote:
> On Sat, Feb 20, 2010 at 4:55 PM, marwie wrote:
> > Hello,
> >
On Sat, Feb 20, 2010 at 4:55 PM, marwie wrote:
> Hello,
>
> I recently read about augmented assignments and that (with l1, l2
> being lists)
>
> l1.extend(l2)
>
> is more efficient than
>
> l1 = l1 + l2
>
> because unnecessary copy operations can be avoided. Now my question is
> if there's a
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