This question already has answers here:
Weird timezone issue with pytz
(3 answers)
Python datetime object show wrong timezone offset
(2 answers)
Closed 13 days ago.
Consider the following:
from datetime import datetime
import pytz
new_years_in_new_york = datetime(
year=2020,
month=1,
day=1,
hour=0,
minute=0,
tzinfo = pytz.timezone('US/Eastern'))
I now I have a datetime object representing January 1, midnight, in New York. Oddly, if I use pytz to convert this to UTC, I'll get an odd datetime off by several minutes:
new_years_in_new_york.astimezone(pytz.utc)
# datetime.datetime(2020, 1, 1, 4, 56, tzinfo=<UTC>)
Notice that midnight in New York, in pytz, is 4:56 in UTC. Elsewhere on Stack Overflow, I learned that's because pytz uses your /usr/share/zoneinfo data, which uses local mean time to account for timezones before standardization. This can be shown here:
pytz.timezone('US/Eastern')
# <DstTzInfo 'US/Eastern' LMT-1 day, 19:04:00 STD>
See that LMK-1 day, 19:04:00 STD? That's a local mean time offset, not the offset I want, which is US/Eastern not during daylight savings time.
Is there a way I can force pytz to use what is currently the standard set of offsets based on a current date? On New Years 2020, it should just be UTC-5. If the date I supplied were during daylight savings time, I would want UTC-4. I'm confused as to why pytz would use a LMT-based offset for a 2020 date.
>>> new_years_in_new_york
datetime.datetime(2020, 1, 1, 0, 0, tzinfo=<DstTzInfo 'US/Eastern' LMT-1 day, 19:04:00 STD>)
Notice the odd offset in that datetime. You're not creating this datetime correctly.
This library only supports two ways of building a localized time. The
first is to use the localize() method provided by the pytz library.
This is used to localize a naive datetime (datetime with no timezone
information):
>>> loc_dt = eastern.localize(datetime(2002, 10, 27, 6, 0, 0))
>>> print(loc_dt.strftime(fmt))
2002-10-27 06:00:00 EST-0500
The second way of building a localized time is by converting an
existing localized time using the standard astimezone() method:
>>> ams_dt = loc_dt.astimezone(amsterdam)
>>> ams_dt.strftime(fmt)
'2002-10-27 12:00:00 CET+0100'
Unfortunately using the tzinfo argument of the standard datetime
constructors ‘’does not work’’ with pytz for many timezones.
>>> datetime(2002, 10, 27, 12, 0, 0, tzinfo=amsterdam).strftime(fmt)
'2002-10-27 12:00:00 LMT+0020'
http://pytz.sourceforge.net/#localized-times-and-date-arithmetic
Related
This question already has answers here:
Weird timezone issue with pytz
(3 answers)
Python datetime object show wrong timezone offset
(2 answers)
Closed 12 days ago.
Consider the following:
from datetime import datetime
import pytz
new_years_in_new_york = datetime(
year=2020,
month=1,
day=1,
hour=0,
minute=0,
tzinfo = pytz.timezone('US/Eastern'))
I now I have a datetime object representing January 1, midnight, in New York. Oddly, if I use pytz to convert this to UTC, I'll get an odd datetime off by several minutes:
new_years_in_new_york.astimezone(pytz.utc)
# datetime.datetime(2020, 1, 1, 4, 56, tzinfo=<UTC>)
Notice that midnight in New York, in pytz, is 4:56 in UTC. Elsewhere on Stack Overflow, I learned that's because pytz uses your /usr/share/zoneinfo data, which uses local mean time to account for timezones before standardization. This can be shown here:
pytz.timezone('US/Eastern')
# <DstTzInfo 'US/Eastern' LMT-1 day, 19:04:00 STD>
See that LMK-1 day, 19:04:00 STD? That's a local mean time offset, not the offset I want, which is US/Eastern not during daylight savings time.
Is there a way I can force pytz to use what is currently the standard set of offsets based on a current date? On New Years 2020, it should just be UTC-5. If the date I supplied were during daylight savings time, I would want UTC-4. I'm confused as to why pytz would use a LMT-based offset for a 2020 date.
>>> new_years_in_new_york
datetime.datetime(2020, 1, 1, 0, 0, tzinfo=<DstTzInfo 'US/Eastern' LMT-1 day, 19:04:00 STD>)
Notice the odd offset in that datetime. You're not creating this datetime correctly.
This library only supports two ways of building a localized time. The
first is to use the localize() method provided by the pytz library.
This is used to localize a naive datetime (datetime with no timezone
information):
>>> loc_dt = eastern.localize(datetime(2002, 10, 27, 6, 0, 0))
>>> print(loc_dt.strftime(fmt))
2002-10-27 06:00:00 EST-0500
The second way of building a localized time is by converting an
existing localized time using the standard astimezone() method:
>>> ams_dt = loc_dt.astimezone(amsterdam)
>>> ams_dt.strftime(fmt)
'2002-10-27 12:00:00 CET+0100'
Unfortunately using the tzinfo argument of the standard datetime
constructors ‘’does not work’’ with pytz for many timezones.
>>> datetime(2002, 10, 27, 12, 0, 0, tzinfo=amsterdam).strftime(fmt)
'2002-10-27 12:00:00 LMT+0020'
http://pytz.sourceforge.net/#localized-times-and-date-arithmetic
This question already has answers here:
How to add timezone into a naive datetime instance in python [duplicate]
(2 answers)
Closed 7 years ago.
I ran across an interesting situation today. Can anyone explain why the offsets for ts1 and ts2 are different? ts1 is a datetime object that is timezone-aware right off the bat. ts2 is a datetime object that starts off timezone-naive and has its tzinfo replaced. However, they end up with different offsets.
>>> from pytz import timezone
>>> EST = timezone('America/New_York')
>>> ts1 = datetime.datetime.now(tz=EST)
>>> ts2 = datetime.datetime.now()
>>> ts2 = ts2.replace(tzinfo=EST)
>>> print ts1
2014-05-16 11:25:16.749748-04:00
>>> print ts2
2014-05-16 11:25:19.581710-05:00
When you call ts2.replace(tzinfo=EST), the tzinfo object you're getting doesn't match the one you get with ts1:
>>> ts1
datetime.datetime(2014, 5, 16, 11, 51, 7, 916090, tzinfo=<DstTzInfo 'America/New_York' EDT-1 day, 20:00:00 DST>)
>>> ts2
datetime.datetime(2014, 5, 16, 11, 51, 30, 922692, tzinfo=<DstTzInfo 'America/New_York' LMT-1 day, 19:04:00 STD>)
You end up with LMT instead of EDT.
The pytz documentation actually notes that using pytz with the tzinfo argument of standard datetime objects simply doesn't work for many timezones:
Unfortunately using the tzinfo argument of the standard datetime
constructors ''does not work'' with pytz for many timezones.
>>> datetime(2002, 10, 27, 12, 0, 0, tzinfo=amsterdam).strftime(fmt) '2002-10-27 12:00:00 LMT+0020'
It is safe for timezones without daylight saving transitions though,
such as UTC:
>>> datetime(2002, 10, 27, 12, 0, 0, tzinfo=pytz.utc).strftime(fmt) '2002-10-27 12:00:00 UTC+0000'
I'm not exactly sure why the first one works; perhaps because it doesn't actually have to convert anything when the object is initially constructed with the tzinfo object.
Edit:
Ah, the Python documentation notes that using datetime.datetime.now() with the tz arg is equivalent to:
EST.fromutc(datetime.utcnow().replace(tzinfo=EST))
Which means you're converting from UTC, which is safe with pytz. So that's why the first one works.
According to the documentation, the correct way to apply a time zone to a naive datetime is with the localize method.
ts1 = eastern.localize(datetime.datetime.now())
Also, I recommend you use avoid EST as a variable name, since it typically standard for "Eastern Standard Time", and America/New_York comprises both "Eastern Standard Time" (EST) and "Eastern Daylight Time" (EDT).
pytz asks you to use the .astimezone method for all time conversion to and from UTC. However, in one special case — datetime.fromtimestamp — it looks like you should be able to use the Python library's datetime methods.
It seems to work here:
>>> import datetime
>>> import pytz
>>> ambigtime = 1352017800 # http://www.wolframalpha.com/input/?i=1352017800+unix+time+in+Los+Angeles
>>> amla = pytz.timezone('America/Los_Angeles')
>>> datetime.datetime.fromtimestamp(ambigtime, tz=amla)
datetime.datetime(2012, 11, 4, 1, 30, tzinfo=<DstTzInfo 'America/Los_Angeles' PDT-1 day, 17:00:00 DST>)
>>> datetime.datetime.fromtimestamp(ambigtime + 3600, tz=amla)
datetime.datetime(2012, 11, 4, 1, 30, tzinfo=<DstTzInfo 'America/Los_Angeles' PST-1 day, 16:00:00 STD>)
Are there situations where datetime.fromtimestamp won't give you the correct results with pytz timezones?
As far as I know, pytz.timezone() will give you an instance of tzinfo (or rather a subclass thereof), and as such is totally fine to use with datetime.fromtimestamp().
As long as pytz has updated zoneinfo files, you can create localized datetimes using that method. Converting a datetime between two zones however is really loads easier to do with the astimezone() method. If I am correct, it basically switches the tzinfo property on the datetime.
I am writing a program which deals a lot with timezones and crossing them. The two things I deal with most are creating a datetime object from "now" and then localizing a naive datetime object.
To create a datetime object from now in the pacific timezone, I am currently doing this (python 2.7.2+)
from datetime import datetime
import pytz
la = pytz.timezone("America/Los_Angeles")
now = datetime.now(la)
Is this correct with regards to DST? If not, I suppose I should be doing:
now2 = la.localize(datetime.now())
My question is why? Can anyone show me a case where the first is wrong and the seconds is right?
As for my seconds question, suppose I had a naive date and time from some user input for 9/1/2012 at 8:00am in Los Angeles, CA. Is the right way to make the datetime like this:
la.localize(datetime(2012, 9, 1, 8, 0))
If not, how should I be building these datetimes?
From the pytz documentation:
The preferred way of dealing with times is to always work in UTC, converting to localtime only when generating output to be read by humans.
So ideally you should be using utcnow instead of now.
Assuming for some reason that your hands are tied and you need to work with local times, you can still run into a problem with trying to localize the current time if you're doing it during the daylight saving transition window. The same datetime might occur twice, once during daylight time and again during standard time, and the localize method doesn't know how to settle the conflict unless you tell it explicitly with the is_dst parameter.
So to get the current UTC time:
utc = pytz.timezone('UTC')
now = utc.localize(datetime.datetime.utcnow())
And to convert it to your local time (but only when you must):
la = pytz.timezone('America/Los_Angeles')
local_time = now.astimezone(la)
Edit: as pointed out in the comments by #J.F. Sebastian, your first example using datetime.now(tz) will work in all cases. Your second example fails during the fall transition as I outlined above. I still advocate using UTC instead of local time for everything except display.
The first solution is correct with regards to DST, and the second solution is bad.
I'll give an example. Here in Europe, when running this code:
from datetime import datetime
import pytz # $ pip install pytz
la = pytz.timezone("America/Los_Angeles")
fmt = '%Y-%m-%d %H:%M:%S %Z%z'
now = datetime.now(la)
now2 = la.localize(datetime.now())
now3 = datetime.now()
print(now.strftime(fmt))
print(now2.strftime(fmt))
print(now3.strftime(fmt))
I get the following:
2012-08-30 12:34:06 PDT-0700
2012-08-30 21:34:06 PDT-0700
2012-08-30 21:34:06
datetime.now(la) creates a datetime with the current time in LA, plus the timezone information for LA.
la.localize(datetime.now()) adds timezone information to the naive datetime, but does no timezone conversion; it just assumes the time was already in this timezone.
datetime.now() creates a naive datetime (without timezone information) with the local time.
As long as you are in LA, you will not see the difference, but if your code ever runs somewhere else, it will probably not do what you wanted.
Apart from that, if you ever need to deal seriously with timezones, it is better to have all your times in UTC, saving yourself a lot of trouble with DST.
This works:
# naive datetime
d = datetime.datetime(2016, 11, 5, 16, 43, 45)
utc = pytz.UTC # UTC timezone
pst = pytz.timezone('America/Los_Angeles') # LA timezone
# Convert to UTC timezone aware datetime
d = utc.localize(d)
>>> datetime.datetime(2016, 11, 5, 16, 43, 45, tzinfo=<UTC>)
# show as in LA time zone (not converting here)
d.astimezone(pst)
>>> datetime.datetime(2016, 11, 5, 9, 43, 45,
tzinfo=<DstTzInfo 'America/Los_Angeles' PDT-1 day, 17:00:00 DST>)
# we get Pacific Daylight Time: PDT
# add 1 day to UTC date
d = d + datetime.timedelta(days=1)
>>> datetime.datetime(2016, 11, 6, 16, 43, 45, tzinfo=<UTC>)
d.astimezone(pst) # now cast to LA time zone
>>> datetime.datetime(2016, 11, 6, 8, 43, 45,
tzinfo=<DstTzInfo 'America/Los_Angeles' PST-1 day, 16:00:00 STD>)
# Daylight saving is applied -> we get Pacific Standard Time PST
This DOES NOT work:
# naive datetime
d = datetime.datetime(2016, 11, 5, 16, 43, 45)
utc = pytz.UTC # UTC timezone
pst = pytz.timezone('America/Los_Angeles') # LA timezone
# convert to UTC timezone aware datetime
d = utc.localize(d)
>>> datetime.datetime(2016, 11, 5, 16, 43, 45, tzinfo=<UTC>)
# convert to 'America/Los_Angeles' timezone: DON'T DO THIS
d = d.astimezone(pst)
>>> datetime.datetime(2016, 11, 5, 9, 43, 45,
tzinfo=<DstTzInfo 'America/Los_Angeles' PDT-1 day, 17:00:00 DST>)
# we are in Pacific Daylight Time PDT
# add 1 day to LA local date: DON'T DO THAT
d = d + datetime.timedelta(days=1)
>>> datetime.datetime(2016, 11, 6, 9, 43, 45,
tzinfo=<DstTzInfo 'America/Los_Angeles' PDT-1 day, 17:00:00 DST>)
# Daylight Saving is NOT respected, we are still in PDT time, not PST
Conclusion:
datetime.timedelta() DOES NOT account for daylight saving.
Do your time add/subtract in UTC timezone ALWAYS.
Cast to local time only for output / display.
The pytz website says:
Unfortunately using the tzinfo argument of the standard datetime
constructors ‘’does not work’’ with pytz for many timezones.
So you should not use datetime.now(la). I don't know the specifics, but some timezones operate on more exotic rules then we are used to, and python's datetime code can't handle them. By using pytz's code, they should be handled correctly since that's pytz's purpose. It may also have issues for the times that occur twice thanks to jumping times in daylight savings.
As for the second question, that's exactly what the documentation shows, so you should be good.
When creating a datetime object in a specific time zone using pytz I get a different UTC offset depending on whether I use datetime.datetime() or datetime.datetime.now().
now() seems to give the correct UTC offset for the time zone, datetime() gives an offset that I don't recognise.
Why are they different? What is the significance of the offset that datetime() assigns?
Here's my code:
import datetime
import pytz
la_paz = pytz.timezone('America/La_Paz')
a = datetime.datetime.now(la_paz)
print a, a.utcoffset()
# 2011-03-22 05:30:13-04:00 -1 day, 20:00:00
# -4 hours is the correct UTC offset for La Paz
b = datetime.datetime(2011, 03, 22, 5, 30, tzinfo=la_paz)
print b, b.utcoffset()
# 2011-03-22 05:30:00-04:33 -1 day, 19:27:00
# What is the significance of -4:33?
It seems that datetime() will use the first recorded timezone for the region by default, and in many cases (like in La Paz) this is old and no longer valid.
The datetime must instead be created naive and then localised like so:
b = la_paz.localize(datetime.datetime(2011, 03, 22, 5, 30))
print b, b.utcoffset()
now() appears to do the localization automatically.
From the pytz documentation:
This library only supports two ways of building a localized time. The first is to use the localize() method provided by the pytz library. This is used to localize a naive datetime (datetime with no timezone information):
>>> loc_dt = eastern.localize(datetime(2002, 10, 27, 6, 0, 0))
>>> print loc_dt.strftime(fmt)
2002-10-27 06:00:00 EST-0500
The second way of building a localized time is by converting an existing localized time using the standard astimezone() method:
>>> ams_dt = loc_dt.astimezone(amsterdam)
>>> ams_dt.strftime(fmt)
'2002-10-27 12:00:00 CET+0100'
Or put another way:
b = datetime.datetime(2011, 03, 22, 5, 30, tzinfo=la_paz)
Is not supported by pytz