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[Python-Dev] PEP 410 (Decimal timestamp): the implementation is ready for a review


On Wed, 15 Feb 2012 20:56:26 +0100
"Martin v. L?wis" <martin at v.loewis.de> wrote:
> 
> With the quartz in Victor's machine, a single clock takes 0.3ns, so
> three of them make a nanosecond. As the quartz may not be entirely
> accurate (and also as the CPU frequency may change) you have to measure
> the clock rate against an external time source, but Linux has
> implemented algorithms for that. On my system, dmesg shows
> 
> [    2.236894] Refined TSC clocksource calibration: 2793.000 MHz.
> [    2.236900] Switching to clocksource tsc

But that's still not meaningful. By the time clock_gettime() returns,
an unpredictable number of nanoseconds have elapsed, and even more when
returning to the Python evaluation loop.

So the nanosecond precision is just an illusion, and a float should
really be enough to represent durations for any task where Python is
suitable as a language.

Regards

Antoine.