Why does datetime datetime utcnow not contain timezone information

Question

datetime datetime utcnow     Why does this datetime not have any timezone info given that it is explicitly a UTC datetime   I would expect that this would contain tzinfo

User · Answer

To add timezone information in Python 3 2   import datetime   gt  gt  gt  d   datetime datetime now tz datetime timezone utc   gt  gt  gt  print d tzinfo   UTC 00 00

User · Answer

The standard Python libraries don t include any tzinfo classes  but see pep 431   I can only guess at the reasons  Personally I think it was a mistake not to include a tzinfo class for UTC  because that one is uncontroversial enough to have a standard implementation   Edit  Although there s no implementation in the library  there is one given as an example in the tzinfo documentation   from datetime import timedelta  tzinfo  ZERO   timedelta 0     A UTC class   class UTC tzinfo          UTC         def utcoffset self  dt           return ZERO      def tzname self  dt           return  UTC       def dst self  dt           return ZERO  utc   UTC     To use it  to get the current time as an aware datetime object   from datetime import datetime   now   datetime now utc    There is datetime timezone utc in Python 3 2    from datetime import datetime  timezone   now   datetime now timezone utc

User · Answer

The behaviour of datetime datetime utcnow   returning UTC time as naive datetime object is obviously problematic and must be fixed  It can lead to unexpected result if your system local timezone is not UTC  since datetime library presume naive datetime object to represent system local time  For example  datetime datetime utcnow   timestaamp   gives timestamp of 4 hours ahead from correct value on my computer  Also  as of python 3 6  datetime astimezone   can be called on naive datetime instances  but datetime datetime utcnow   astimezone any timezone  gives wrong result unless your system local timezone is UTC

User · Answer

The pytz module is one option  and there is another python-dateutil  which although is also third party package  may already be available depending on your other dependencies and operating system   I just wanted to include this methodology for reference- if you ve already installed python-dateutil for other purposes  you can use its tzinfo instead of duplicating with pytz  import datetime import dateutil tz    Get the UTC time with datetime now  utcdt   datetime datetime now dateutil tz tzutc       Get the UTC time with datetime utcnow  utcdt   datetime datetime utcnow   utcdt   utcdt replace tzinfo dateutil tz tzutc       For fun- get the local time localdt   datetime datetime now dateutil tz tzlocal      I tend to agree that calls to utcnow should include the UTC timezone information  I suspect that this is not included because the native datetime library defaults to naive datetimes for cross compatibility

User · Answer

from datetime import datetime  from dateutil relativedelta import relativedelta d   datetime now   date   datetime isoformat d  split      0  d month   datetime today     relativedelta months 1  next month   datetime isoformat d month  split      0

User · Answer

UTC dates don t need any timezone info since they re UTC  which by definition means that they have no offset

User · Answer

Note that for Python 3 2 onwards  the datetime module contains datetime timezone  The documentation for datetime utcnow   says   An aware current UTC datetime can be obtained by calling datetime now timezone utc    So  datetime utcnow   doesn t set tzinfo to indicate that it is UTC  but datetime now datetime timezone utc  does return UTC time with tzinfo set  So you can do   gt  gt  gt  import datetime  gt  gt  gt  datetime datetime now datetime timezone utc  datetime datetime 2014  7  10  2  43  55  230107  tzinfo datetime timezone utc

User · Answer

Julien Danjou wrote a good article explaining why you should never deal with timezones  An excerpt      Indeed  Python datetime API always returns unaware datetime objects    which is very unfortunate  Indeed  as soon as you get one of this   object  there is no way to know what the timezone is  therefore these   objects are pretty  useless  on their own    Alas  even though you may use utcnow    you still won t see the timezone info  as you discovered   Recommendations         Always use aware datetime objects  i e  with timezone information  That   makes sure you can compare them directly  aware and unaware datetime   objects are not comparable  and will return them correctly to users    Leverage pytz to have timezone objects     Use ISO 8601 as the input and   output string format  Use datetime datetime isoformat   to return   timestamps as string formatted using that format  which includes the   timezone information    If you need to parse strings containing ISO 8601 formatted timestamps    you can rely on iso8601  which returns timestamps with correct   timezone information  This makes timestamps directly comparable

User · Answer

That means it is timezone naive  so you can t use it with datetime astimezone  you can give it a timezone like this  import pytz    3rd party    pip install pytz  u   datetime utcnow   u   u replace tzinfo pytz utc   NOTE  it works only with a fixed utc offset   now you can change timezones  print u astimezone pytz timezone  America New York       To get the current time in a given timezone  you could pass tzinfo to datetime now   directly      usr bin env python from datetime import datetime import pytz     pip install pytz  print datetime now pytz timezone  America New York       It works for any timezone including those that observe daylight saving time  DST  i e   it works for timezones that may have different utc offsets at different times  non-fixed utc offset   Don t use tz localize datetime now    -- it may fail during end-of-DST transition when the local time is ambiguous

[python] Why does datetime.datetime.utcnow() not contain timezone information?

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