Re: SVN: Zope/trunk/ Optimized the `OFS.Traversable.getPhysicalPath` method to avoid excessive amounts of method calls. Thx to Nikolay Kim from Enfold

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On 07/14/2011 11:47 AM, Tres Seaver wrote:

> While we're at it, 'list.insert(0,foo)' is known to be slower in a
> tight loop than 'list.append(foo)', with a 'reversed' at the end of
> the loop::
> 
> $ python -m timeit -s "from string import letters" "path = []" \ "for
> letter in letters: path.append(letter)" \ "result =
> tuple(reversed(path))" 100000 loops, best of 3: 15.9 usec per loop
> 
> $ python -m timeit -s "from string import letters" "path = []" \ "for
> letter in letters: path.insert(0, letter)" \ "result = tuple(path)" 
> 10000 loops, best of 3:  25.3 usec per loop
> 
> 
> For the sake of comparison, the original tuple addition is actually 
> between the two:
> 
> $ python -m timeit -s "from string import letters" "result = ()" \ 
> "for letter in letters: result += (letter,)" 10000 loops, best of 3:
> 21.6 usec per loop

A further micro-optimization is to pre-allocate a big list in a thread
local.  Running the attached script produces::

 $ python perftest.py
 Via insert_0: 24.8401839733
 Via append: 15.6596238613
   speedup: 37.0%
 Via tuple_add: 21.9555268288
   speedup: 11.6%
 Via prealloc: 10.5278339386
   speedup: 57.6%



Tres.
- -- 
===================================================================
Tres Seaver          +1 540-429-0999          [email protected]
Palladion Software   "Excellence by Design"    http://palladion.com
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from string import letters
from threading import local

def via_append():
    path = []
    for letter in letters:
        path.append(letter)
    return tuple(reversed(path))
    
def via_insert_0():
    path = []
    for letter in letters:
        path.insert(0, letter)
    return tuple(path)

def via_tuple_add():
    result = ()
    for letter in letters:
        result += (letter,)
    return result

prealloc = local()
def via_prealloc():
    items = getattr(prealloc, 'items', None)
    if items is None:
        items = prealloc.items = [None] * 1000
    count = 0
    for letter in letters:
        items[count] = letter
        count += 1
    return tuple(items[:count])

if __name__ == '__main__':
    from timeit import Timer
    insert_0 = min(Timer(via_insert_0).repeat())
    print 'Via insert_0:', insert_0

    append = min(Timer(via_append).repeat())
    print 'Via append:', append
    print '  speedup: %0.1f%%' % ((insert_0 - append) / insert_0 * 100)

    tuple_add = min(Timer(via_tuple_add).repeat())
    print 'Via tuple_add:', tuple_add
    print '  speedup: %0.1f%%' % ((insert_0 - tuple_add) / insert_0 * 100)

    prealloc = min(Timer(via_prealloc).repeat())
    print 'Via prealloc:', prealloc
    print '  speedup: %0.1f%%' % ((insert_0 - prealloc) / insert_0 * 100)