How do you convert a timestamp into a datetime in python with the correct timezone? -

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you naively expect work:

import pytz datetime import datetime def tz_datetime_from_timestamp(timestamp):     """convert timestamp datetime """     tz = pytz.timezone('australia/perth')     server_time = datetime.utcnow()     delta = tz.utcoffset(server_time)     value = datetime.utcfromtimestamp(timestamp).replace(tzinfo=tz)     return value + delta  print tz_datetime_from_timestamp(1416387060)

and convert timestamp 1416387060 wed nov 19 16:51:00 2014 gmt+8:00.

...but not. prints:

2014-11-19 16:51:00+07:43

the timezone of australia/perth not gmt+7:43.

it gmt+8:00. unequivocally stated on australian government website http://www.australia.gov.au/about-australia/our-country/time:

awst equal coordinated universal time plus 8 hours (utc +8).

so, heck pytz pulling 7.43 from?

well, turns out pytz pulls data http://www.iana.org/time-zones time zone database, , database states:

# western australia # # rule  name    type  in  on  @  save  letter/s rule  aw  1974   - oct lastsun 2:00s 1:00  d rule  aw  1975   - mar sun>=1  2:00s 0 s rule  aw  1983   - oct lastsun 2:00s 1:00  d rule  aw  1984   - mar sun>=1  2:00s 0 s rule  aw  1991   - nov 17  2:00s 1:00  d rule  aw  1992   - mar sun>=1  2:00s 0 s rule  aw  2006   - dec  3  2:00s 1:00  d rule  aw  2007  2009  - mar lastsun 2:00s 0 s rule  aw  2007  2008  - oct lastsun 2:00s 1:00  d zone australia/perth   7:43:24 -  lmt 1895 dec        8:00 aus aw%st 1943 jul        8:00 aw  aw%st

well. that's great.... it's incorrect.

...and python, result, unfortunately.

the olson time database full of values like (4 hours , 15 minutes, 5 hours , 20 minutes, etc.). totally weird.

technically don't care exact timezone is, long universally consistent; unfortunately it's not. making (for example) api call , passing timezone across remote service (correctly) uses gmt+8 timezone results in discrepancy between values when timezones converted utc processing.

ie. absolutely clear, these 2 values different times when converted utc:

  • wed nov 19 16:51:00 2014 gmt+8:00
  • wed nov 19 16:51:00 2014 gmt+7:43

irritatingly:

server_time = datetime.utcnow() delta = tz.utcoffset(server_time) print(delta)

yields:

8:00:00

so pytz internally does know correct timezone offset. generates output wrong value attached.

so, finally: how generate datetime correct timezone attached it?

the long story short, pytz defaults incorrect timezone, , datetime.replace() doesn't perform conversions:

import pytz datetime import datetime  fmt = '%y-%m-%d %h:%m:%s %z%z' tz = pytz.timezone('australia/perth') timestamp = 1416387060 print(tz)  # correct way utctime = pytz.utc.localize(datetime.utcfromtimestamp(timestamp)) print(utctime.strftime(fmt))  astimezone = utctime.astimezone(tz) print(astimezone.strftime(fmt))  localtime = tz.normalize(astimezone) print(localtime.strftime(fmt))  # incorrect way incorrect = datetime.utcfromtimestamp(timestamp).replace(tzinfo=tz) print(incorrect.strftime(fmt))

you can read more in various bugs in pytz in discussed:


Comments

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