[Python-Dev] PEP 418 is too divisive and confusing and should be postponed

Cameron Simpson cs at zip.com.au
Sun Apr 8 00:39:25 CEST 2012

On 07Apr2012 20:40, Steven D'Aprano <steve at pearwood.info> wrote:
| Victor Stinner wrote:
| > I don't think that NTP works like that. NTP only uses very smooth adjustements:
| > http://www.python.org/dev/peps/pep-0418/#ntp-adjustment
| That is incorrect. NTP by default will only slew the clock for small 
| discrepancies. For large discrepancies, it will step the clock, causing the 
| time to jump. By default, "large" here means more than 128 milliseconds.
| Yes, milliseconds.
| http://www.ntp.org/ntpfaq/NTP-s-config-tricks.htm#AEN4249
| In any case, NTP is not the only thing that adjusts the clock, e.g. the 
| operating system will adjust the time for daylight savings.

Ignoring the discussion of NTP, daylight saving is a _presentation_
issue. It is _display_. The OS clock does not change for daylight
saving! Think: "seconds since the epoch". This is a continuous function.
Daylight saving presentation occurs turning a seconds-since-epoch into a
human decomposed time (hours, etc).

Now, AFAIR, Windows used to run its system clock in "local time"
i.e. it did have to jump its clock for daylight saving. Hopefully that
is long gone.

UNIX never did this. It ran in seconds since the epoch (in its case, start of
01jan1970 GMT). Printing dates and timestamps to humans needed daylight
saving knowledge etc.

Cameron Simpson <cs at zip.com.au> DoD#743

Stan Malyshev <stas at netcom.com> wrote:
| You're dragging a peg in a blind hairpin when you see a patch of coolant
| up ahead, and you hear the airbrakes of an oncoming 18-wheeler.
| What do you do?  WHAT DO YOU DO?  ("Speed", anyone?)
Shoot my pillion?       - Vociferous Mole <stevegr at Starbase.NeoSoft.COM>

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