Art Art - 1 month ago 21
Python Question

pytz utc conversion

What is the right way to convert a naive time and a

tzinfo
into an utc time?
Say I have:

d = datetime(2009, 8, 31, 22, 30, 30)
tz = timezone('US/Pacific')


First way, pytz inspired:

d_tz = tz.normalize(tz.localize(d))
utc = pytz.timezone('UTC')
d_utc = d_tz.astimezone(utc)


Second way, from UTCDateTimeField

def utc_from_localtime(dt, tz):
dt = dt.replace(tzinfo=tz)
_dt = tz.normalize(dt)
if dt.tzinfo != _dt.tzinfo:
# Houston, we have a problem...
# find out which one has a dst offset
if _dt.tzinfo.dst(_dt):
_dt -= _dt.tzinfo.dst(_dt)
else:
_dt += dt.tzinfo.dst(dt)
return _dt.astimezone(pytz.utc)


Needles to say those two methods produce different results for quite a few timezones.

Question is - what's the right way?

Answer

Your first method seems to be the approved one, and should be DST-aware.

You could shorten it a tiny bit, since pytz.utc = pytz.timezone('UTC'), but you knew that already :)

tz = timezone('US/Pacific')
def toUTC(d):
    return tz.normalize(tz.localize(d)).astimezone(pytz.utc)

print "Test: ", datetime.datetime.utcnow(), " = ", toUTC(datetime.datetime.now())