Question

I have a web app that captures date / time via a JS script and calculates seconds since epoch in UTC format – ex 134250270000. In the backend we have a Python script that fetches data from DB but has date / time stored in number of seconds since epoch in PST format. There is always a difference of seconds between UTC and PST if counted from epoch.

Is there any method by which I can convert the UTC seconds since to epoch to PST seconds since epoch? We need to take a note of daylight changes in PST timezone also?

EDIT::

I have the seconds since epoch in UTC format:

1342502700

I found that I get the sum in seconds between UTC and local standard time via:

>>> time.timezone / 3600
8

So If I add 1342502700 to time.timezone:

>>> print 1342502700 + time.timezone
1344153600

Will it always give me PDT / PST times correctly?

EDIT::

Maybe this is the correct one:

>>> import time
>>> offset = time.timezone if (time.daylight == 0) else time.altzone
>>> offset / 60 / 60
7

time.daylight will be non-zero if daylight savings is currently in effect.

Answer 1

I think somewhere in your conversions there’s an implied time zone that’s messing things up. Regardless, I think what you’re looking for is time.altzone:

>>> from time import *
>>> ctime(time())
'Mon Aug 13 16:54:02 2012'
>>> ctime(time()+altzone)
'Mon Aug 13 08:54:04 2012'

I’m on Taipei time right now, so my local time (the first one) is later than UTC.

EDIT: I missed the line in the documentation that says only to use altzone if daylight is non-zero. Apparently it’s a bit more complicated than I thought if you live somewhere with Daylight Savings Time. Refer to this post if you need to deal with that:

Python: get timezone based on DST for a timestamp