[Python-Dev] PEP 418: Add monotonic time, performance counter and process time functions

Chris Angelico rosuav at gmail.com
Tue Apr 17 16:18:41 CEST 2012

On Tue, Apr 17, 2012 at 2:48 PM, Cameron Simpson <cs at zip.com.au> wrote:
> On 16Apr2012 01:25, Victor Stinner <victor.stinner at gmail.com> wrote:
> | I suppose that most people don't care that "resolution" and
> | "precision" are different things.
> If we're using the same definitions we discussed offline, where
>  - resolution is the units the clock call (underneath) works in (for
>    example, nanoseconds)
>  - precision is the effective precision of the results, for example
>    milliseconds
> I'd say people would care if they knew, and mostly care about
> "precision".

Meaning that resolution is a matter of format and API, not of clock.
If you take a C clock API that returns a value in nanoseconds and
return it as a Python float, you've changed the resolution. I don't
think resolution matters much, beyond that (for example) nanosecond
resolution allows a clock to be subsequently upgraded as far as
nanosecond precision without breaking existing code, even if currently
it's only providing microsecond precision. But it makes just as much
sense for your resolution to be 2**64ths-of-a-second or
quarters-of-the-internal-CPU-clock-speed as it does for nanoseconds.
As long as it's some fraction of the SI second, every different
resolution is just a fixed ratio away from every other one.


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