[Python-Dev] PEP 564: Add new time functions with nanosecond resolution

Antoine Pitrou solipsis at pitrou.net
Mon Oct 16 11:06:31 EDT 2017


On Mon, 16 Oct 2017 12:42:30 +0200
Victor Stinner <victor.stinner at gmail.com> wrote:
> ``time.time()`` returns seconds elapsed since the UNIX epoch: January
> 1st, 1970. This function loses precision since May 1970 (47 years ago)::

This is a funny sentence.  I doubt computers (Unix or not) had
nanosecond clocks in May 1970.

> This PEP adds five new functions to the ``time`` module:
> * ``time.clock_gettime_ns(clock_id)``
> * ``time.clock_settime_ns(clock_id, time: int)``
> * ``time.perf_counter_ns()``
> * ``time.monotonic_ns()``
> * ``time.time_ns()``

Why not ``time.process_time_ns()``?

> Hardware clock with a resolution better than 1 nanosecond already
> exists. For example, the frequency of a CPU TSC clock is the CPU base
> frequency: the resolution is around 0.3 ns for a CPU running at 3
> GHz. Users who have access to such hardware and really need
> sub-nanosecond resolution can easyly extend Python for their needs.

Typo: easily.  But how is easy is it?

> Such rare use case don't justify to design the Python standard library
> to support sub-nanosecond resolution.

I suspect that assertion will be challenged at some point :-)
Though I agree with the ease of implementation argument (about int64_t
being wide enough for nanoseconds but not picoseconds).



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