What you need to know about datetimes
[Pages:48]What you need to know about datetimes
Saturday, March 10, 2012
Taavi Burns taavi@ @jaaaarel
Defect Poacher & Futurist
Time is complicated
? I know more about it now than I did 3 weeks ago ? I'll probably know more by the end of PyCon!
Saturday, March 10, 2012
Outline
? What's an "Instant"? ? Time standards ? Timezones ? Python modules: time, calendar, Naive vs Aware
datetimes, pytz ? Interoperability
Saturday, March 10, 2012
An Instant
? "An instant is a infinitesimal moment in time, a moment whose passage is instantaneous." ?
Saturday, March 10, 2012
An Instant
? The instant represented by ? 2012-03-10 10:30:00 PST
? Is the same instant represented by ? 2012-03-10 13:30:00 EST
? Let's get into that...
Saturday, March 10, 2012
Time standards
? "A time standard is a specification for measuring time: either the rate at which time passes; or points in time; or both."
? ? UT1, TAI, UTC, POSIX, ...
Saturday, March 10, 2012
UT1
? Based entirely on Earth's rotation ? Length of a second depends on tides, weather,
incoming comets... ? Earth Rotation Angle =
2(0.7790572732640 + 1.00273781191135448Tu) radians ?
Saturday, March 10, 2012
TAI
? International Atomic Time ? Average of 200 atomic clocks worldwide ? Counts SI seconds: "By definition, radiation produced
by the transition between the two hyperfine ground states of caesium (in the absence of external influences such as the Earth's magnetic field) has a frequency of exactly 9 192 631 770 Hz." ? ? Is drifting ahead of "reality" by keeping a straight beat
Saturday, March 10, 2012
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