Re: Question about `list.insert`

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From	Peter Otten <__peter__@web.de>
Subject	Re: Question about `list.insert`
Date	Fri, 07 Feb 2014 09:25:10 +0100
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cool-RR wrote:

> I'm curious. If I append an item to a list from the left using
> `list.insert`, will Python always move the entire list one item to the
> right (which can be super-slow) or will it check first to see whether it
> can just allocate more memory to the left of the list and put the item
> there, saving a lot of resources?

Let's see:

$ python3.4 -m timeit -s 'a = [None]' 'a.insert(0, None); del a[0]'
1000000 loops, best of 3: 0.596 usec per loop
$ python3.4 -m timeit -s 'a = [None]*1000' 'a.insert(0, None); del a[0]'
100000 loops, best of 3: 2.59 usec per loop
$ python3.4 -m timeit -s 'a = [None]*10000' 'a.insert(0, None); del a[0]'
10000 loops, best of 3: 24.7 usec per loop
$ python3.4 -m timeit -s 'a = [None]*100000' 'a.insert(0, None); del a[0]'
1000 loops, best of 3: 508 usec per loop
$ python3.4 -m timeit -s 'a = [None]*1000000' 'a.insert(0, None); del a[0]'
100 loops, best of 3: 7.61 msec per loop

$ python3.4 -m timeit -s 'from collections import deque; a = 
deque([None]*1000000)' 'a.appendleft(None); a.popleft()'
1000000 loops, best of 3: 0.263 usec per loop

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Thread

Question about `list.insert` cool-RR <ram.rachum@gmail.com> - 2014-02-06 15:59 -0800
  Re: Question about `list.insert` Terry Reedy <tjreedy@udel.edu> - 2014-02-06 19:40 -0500
  Re: Question about `list.insert` MRAB <python@mrabarnett.plus.com> - 2014-02-07 00:42 +0000
  Re: Question about `list.insert` Terry Reedy <tjreedy@udel.edu> - 2014-02-06 21:48 -0500
  Re:Question about `list.insert` Dave Angel <davea@davea.name> - 2014-02-06 21:54 -0500
    Re: Question about `list.insert` Roy Smith <roy@panix.com> - 2014-02-06 22:00 -0500
      Re: Question about `list.insert` Rustom Mody <rustompmody@gmail.com> - 2014-02-06 19:08 -0800
      Re: Question about `list.insert` Tim Chase <python.list@tim.thechases.com> - 2014-02-06 21:11 -0600
        Re: Question about `list.insert` Roy Smith <roy@panix.com> - 2014-02-06 22:12 -0500
          Re: Question about `list.insert` Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-02-07 17:18 +1300
      Re: Question about `list.insert` Chris Angelico <rosuav@gmail.com> - 2014-02-07 14:14 +1100
      Re: Question about `list.insert` Chris Angelico <rosuav@gmail.com> - 2014-02-07 14:20 +1100
        Re: Question about `list.insert` Rustom Mody <rustompmody@gmail.com> - 2014-02-06 19:29 -0800
          Re: Question about `list.insert` Chris Angelico <rosuav@gmail.com> - 2014-02-07 14:45 +1100
      Re: Question about `list.insert` Asaf Las <roegltd@gmail.com> - 2014-02-06 19:28 -0800
  Re: Question about `list.insert` Dan Stromberg <drsalists@gmail.com> - 2014-02-06 20:52 -0800
    Re: Question about `list.insert` Asaf Las <roegltd@gmail.com> - 2014-02-06 21:18 -0800
  Re: Question about `list.insert` Peter Otten <__peter__@web.de> - 2014-02-07 09:25 +0100

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