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References: <m22emv$ki$1@ger.gmane.org>
Date: Mon, 20 Oct 2014 18:58:28 +1100
Subject: Re: time.perf_counter in Python 2?
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
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On Mon, Oct 20, 2014 at 6:47 PM, Florian Lindner <mailinglists@xgm.de> wrot=
e:
> time.clock()
> On Unix, return the current processor time as a floating point number
> expressed in seconds. The precision, and in fact the very definition of t=
he
> meaning of =E2=80=9Cprocessor time=E2=80=9D, depends on that of the C fun=
ction of the same
> name, but in any case, this is the function to use for benchmarking Pytho=
n
> or timing algorithms.
>
> But for me it always returns the almost same number, nothing time like:

You're doing practically no work in there. You're using almost no
processor time - the interpreter's waiting for the user, not actually
busy. If you create a busyloop, you'll see time.clock() go up roughly
linearly:

rosuav@sikorsky:~$ python
Python 2.7.3 (default, Mar 13 2014, 11:03:55)
[GCC 4.7.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import time
>>> def killtime():
...     start=3Dtime.time()
...     end=3Dtime.clock()+1
...     while time.clock()<end: pass
...     return time.time()-start
...
>>> killtime()
1.0048420429229736
>>> killtime()
1.004641056060791
>>> killtime()
1.0081689357757568
>>> killtime()
1.0019969940185547
>>> killtime()
1.0044770240783691

This function will do its best to waste one second of CPU time. As you
see, it's taking pretty much exactly one second of wall time to do so
(as measured by time.time()). At the end of a few of these runs,
time.clock() will return a value that's fairly close to 1.0 times the
number of executions of killtime(), as the other work Python's doing
is insignificant by comparison.

ChrisA