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

Antoine Pitrou solipsis at pitrou.net
Wed Feb 15 21:06:43 CET 2012

On Wed, 15 Feb 2012 20:56:26 +0100 "Martin v. Löwis" <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.

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