[Python-Dev] this is why we shouldn't call it a "monotonic clock" (was: PEP 418 is too divisive and confusing and should be postponed)

Guido van Rossum guido at python.org
Fri Apr 6 17:42:57 CEST 2012


I'd like to veto wall clock because to me that's the clock on my wall, i.e.
local time. Otherwise I like the way this thread is going.

--Guido van Rossum (sent from Android phone)
On Apr 6, 2012 4:57 AM, "Paul Moore" <p.f.moore at gmail.com> wrote:

> On 6 April 2012 11:12, Steven D'Aprano <steve at pearwood.info> wrote:
>
>> Glyph Lefkowitz wrote:
>>
>>> On Apr 5, 2012, at 8:07 PM, Zooko Wilcox-O'Hearn wrote:
>>>
>>
>>  2. Those who think that "monotonic clock" means a clock that never jumps,
>>>> and that runs at a rate approximating the rate of real time. This is a
>>>> very useful kind of clock to have! It is what C++ now calls a "steady
>>>> clock". It is what all the major operating systems provide.
>>>>
>>>
>>> All clocks run at a rate approximating the rate of real time.  That is
>>> very
>>> close to the definition of the word "clock" in this context.  All clocks
>>> have flaws in that approximation, and really those flaws are the whole
>>> point of access to distinct clock APIs.  Different applications can cope
>>> with different flaws.
>>>
>>
>> I think that this is incorrect.
>>
>> py> time.clock(); time.sleep(10); time.clock()
>> 0.41
>> 0.41
>>
>
> Blame Python's use of CPU time in clock() on Unix for that. On Windows:
>
> >>> time.clock(); time.sleep(10); time.clock()
> 14.879754156329385
> 24.879591008462793
>
> That''s a backward compatibility issue, though - I'd be arguing that
> time.clock() is the best name for "normally the right clock for interval,
> benchmark or timeout uses as long as you don't care about oddities like
> suspend" otherwise. Given that this name is taken, I'd argue for
> time.wallclock. I'm not familiar enough with the terminology to know what
> to expect from terms like monotonic, steady, raw and the like.
>
> Paul.
>
>
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