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Re: while True or while 1

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Il 23 gennaio 2012 20:12, Erik Max Francis <max@alcyone.com> ha scritto:
> Giampaolo Rodolà wrote:
>>
>> Il 21 gennaio 2012 22:13, Erik Max Francis <max@alcyone.com> ha scritto:
>>>
>>> The real reason people still use the `while 1` construct, I would
>>> imagine,
>>>
>>> is just inertia or habit, rather than a conscious, defensive decision.
>>>  If
>>> it's the latter, it's a case of being _way_ too defensive.
>>
>>
>> It's also because while 1 is faster:
>
>        ...
>>
>> while True: 1.41121292114
>> while 1:      1.07101011276
>>
>> Most of the times tha't won't make any noticeable difference, but it's
>> also true that certain while loops are going to iterate milions of
>> times.
>> Think about receiving a 10 GB file by using a socket. You'd tipically
>> have something like this:
>>
>> while 1:
>>    chunk = sock.recv(1024):
>>    if not chunk:
>>          break
>>     ...
>>
>> Now, that's a case where I (personally) want to explicitly use "while
>>
>> 1" instead of "while True".
>
>
> Such a loop would obviously be I/O-bound, not CPU-bound.  So changing the
> form of the while loop would make minimal difference to its overall
> performance.  It'd be spending the vast majority of its time blocked at the
> OS socket level, not executing the condition of the while loop.
>
> As with most of these things, if one is this worried about performance, then
> either Python was the wrong choice to begin with, or there's a good chance
> that you're worried about something that isn't actually where the bottleneck
> is in the first place.
>
>
> --
> Erik Max Francis && max@alcyone.com && http://www.alcyone.com/max/
>  San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Jabber erikmaxfrancis
>  Think twice before you speak to a friend in need.
>   -- Ambrose Bierce
> --
> http://mail.python.org/mailman/listinfo/python-list

Obviously, you're right. I picked up the wrong example.
My point is 1.41121292114 vs 1.07101011276 *might* make some
difference in certain cases.
I just can't come up with a good example where that would be justified. =)


--- Giampaolo
http://code.google.com/p/pyftpdlib/
http://code.google.com/p/psutil/
http://code.google.com/p/pysendfile/

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Re: while True or while 1 Chris Angelico <rosuav@gmail.com> - 2012-01-22 01:59 +1100
  Re: while True or while 1 Erik Max Francis <max@alcyone.com> - 2012-01-21 13:13 -0800
    Re: while True or while 1 Chris Angelico <rosuav@gmail.com> - 2012-01-22 09:13 +1100
      Re: while True or while 1 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-01-22 05:25 +0000
        Re: while True or while 1 Dan Sommers <dan@tombstonezero.net> - 2012-01-22 16:05 +0000
          Re: while True or while 1 alex23 <wuwei23@gmail.com> - 2012-01-22 19:55 -0800
            Re: while True or while 1 Dave Angel <d@davea.name> - 2012-01-23 08:02 -0500
              Re: while True or while 1 Hrvoje Niksic <hniksic@xemacs.org> - 2012-01-23 14:28 +0100
                Re: while True or while 1 Dave Angel <d@davea.name> - 2012-01-23 13:33 -0500
        Re: while True or while 1 MRAB <python@mrabarnett.plus.com> - 2012-01-22 16:13 +0000
    Re: while True or while 1 Grant Edwards <invalid@invalid.invalid> - 2012-01-23 15:51 +0000
    Re: while True or while 1 Giampaolo Rodolà <g.rodola@gmail.com> - 2012-01-23 17:41 +0100
      Re: while True or while 1 Erik Max Francis <max@alcyone.com> - 2012-01-23 11:12 -0800
        Re: while True or while 1 Giampaolo Rodolà <g.rodola@gmail.com> - 2012-01-23 21:20 +0100
    Re: while True or while 1 Ian Kelly <ian.g.kelly@gmail.com> - 2012-01-23 10:39 -0700
    Re: while True or while 1 Evan Driscoll <edriscoll@wisc.edu> - 2012-01-23 12:05 -0600
    Re: while True or while 1 Andrea Crotti <andrea.crotti.0@gmail.com> - 2012-01-23 20:50 +0000
      Re: while True or while 1 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-23 14:42 -0800
      Re: while True or while 1 88888 Dihedral <dihedral88888@googlemail.com> - 2012-01-23 14:42 -0800
      Re: while True or while 1 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-01-24 03:37 +0000

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