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Re: relative speed of incremention syntaxes (or "i=i+1" VS "i+=1")

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On Sun, 21 Aug 2011 09:52:23 -0700, Laurent wrote:

> I did many tests and "i = i + 1" always seems to be around 2% faster
> than "i += 1". This is no surprise as the += notation seems to be a
> syntaxic sugar layer that has to be converted to i = i + 1 anyway. Am I
> wrong in my interpretation? 

It depends. If the value on the left has an __iadd__ method, that will be
called; the value will be updated in-place, so all references to that
object will be affected:

	> import numpy as np
	> a = np.zeros(3)
	> b = a
	> a
	array([ 0.,  0.,  0.])
	> b
	array([ 0.,  0.,  0.])
	> a += 1
	> a
	array([ 1.,  1.,  1.])
	> b
	array([ 1.,  1.,  1.])

If the value on the left doesn't have an __iadd__ method, then addition is
performed and the name is re-bound to the result:

	> a = a + 1
	> a
	array([ 2.,  2.,  2.])
	> b
	array([ 1.,  1.,  1.])

If you're writing code which could reasonably be expected to work with
arbitrary "numeric" values, you should decide which to use according to
whether in-place modification is appropriate rather than trivial
performance differences. If a difference of a few percent is significant,
Python is probably the wrong language in the first place.

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relative speed of incremention syntaxes (or "i=i+1" VS "i+=1") Laurent <laurent.payot@gmail.com> - 2011-08-21 09:52 -0700
  Re: relative speed of incremention syntaxes (or "i=i+1" VS "i+=1") woooee <woooee@gmail.com> - 2011-08-21 09:59 -0700
    Re: relative speed of incremention syntaxes (or "i=i+1" VS "i+=1") Laurent <laurent.payot@gmail.com> - 2011-08-21 10:03 -0700
      Re: relative speed of incremention syntaxes (or "i=i+1" VS "i+=1") Irmen de Jong <irmen@-NOSPAM-xs4all.nl> - 2011-08-21 19:14 +0200
        Re: relative speed of incremention syntaxes (or "i=i+1" VS "i+=1") Hans Mulder <hansmu@xs4all.nl> - 2011-08-21 19:57 +0200
  Re: relative speed of incremention syntaxes (or "i=i+1" VS "i+=1") Nobody <nobody@nowhere.com> - 2011-08-21 22:07 +0100
    Re: relative speed of incremention syntaxes (or "i=i+1" VS "i+=1") Laurent Payot <laurent.payot@gmail.com> - 2011-08-21 16:49 -0700
      Re: relative speed of incremention syntaxes (or "i=i+1" VS "i+=1") Terry Reedy <tjreedy@udel.edu> - 2011-08-21 22:15 -0400
    Re: relative speed of incremention syntaxes (or "i=i+1" VS "i+=1") Terry Reedy <tjreedy@udel.edu> - 2011-08-21 20:35 -0400

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