How to make an unaware datetime timezone aware in python

Question

What I need to do  I have a timezone-unaware datetime object  to which I need to add a time zone in order to be able to compare it with other timezone-aware datetime objects   I do not want to convert my entire application to timezone unaware for this one legacy case   What I ve Tried  First  to demonstrate the problem   Python 2 6 1  r261 67515  Jun 24 2010  21 47 49    GCC 4 2 1  Apple Inc  build 5646   on darwin Type  help    copyright    credits  or  license  for more information   gt  gt  gt  import datetime  gt  gt  gt  import pytz  gt  gt  gt  unaware   datetime datetime 2011 8 15 8 15 12 0   gt  gt  gt  unaware datetime datetime 2011  8  15  8  15  12   gt  gt  gt  aware   datetime datetime 2011 8 15 8 15 12 0 pytz UTC   gt  gt  gt  aware datetime datetime 2011  8  15  8  15  12  tzinfo  lt UTC gt    gt  gt  gt  aware    unaware Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  can t compare offset-naive and offset-aware datetimes   First  I tried astimezone    gt  gt  gt  unaware astimezone pytz UTC  Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  ValueError  astimezone   cannot be applied to a naive datetime  gt  gt  gt    It s not terribly surprising this failed  since it s actually trying to do a conversion   Replace seemed like a better choice  as per Python  How to get a value of datetime today   that is  quot timezone aware quot       gt  gt  gt  unaware replace tzinfo pytz UTC  datetime datetime 2011  8  15  8  15  12  tzinfo  lt UTC gt    gt  gt  gt  unaware    aware Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  TypeError  can t compare offset-naive and offset-aware datetimes  gt  gt  gt     But as you can see  replace seems to set the tzinfo  but not make the object aware   I m getting ready to fall back to doctoring the input string to have a timezone before parsing it  I m using dateutil for parsing  if that matters   but that seems incredibly kludgy   Also  I ve tried this in both python 2 6 and python 2 7  with the same results   Context  I am writing a parser for some data files   There is an old format I need to support where the date string does not have a timezone indicator   I ve already fixed the data source  but I still need to support the legacy data format   A one time conversion of the legacy data is not an option for various business BS reasons   While in general  I do not like the idea of hard-coding a default timezone  in this case it seems like the best option   I know with reasonable confidence that all the legacy data in question is in UTC  so I m prepared to accept the risk of defaulting to that in this case

User · Answer

for those that just want to make a timezone aware datetime  import datetime import pytz  datetime datetime 2019  12  7  tzinfo pytz UTC

User · Answer

Changing between timezones  import pytz from datetime import datetime  other tz   pytz timezone  Europe Madrid      From random aware datetime    aware datetime   datetime utcnow   astimezone other tz   gt  gt  2020-05-21 08 28 26 984948 02 00    1  Change aware datetime to UTC and remove tzinfo to obtain an unaware datetime unaware datetime   aware datetime astimezone pytz UTC  replace tzinfo None   gt  gt  2020-05-21 06 28 26 984948    2  Set tzinfo to UTC directly on an unaware datetime to obtain an utc aware datetime aware datetime utc   unaware datetime replace tzinfo pytz UTC   gt  gt  2020-05-21 06 28 26 984948 00 00    3  Convert the aware utc datetime into another timezone reconverted aware datetime   aware datetime utc astimezone other tz   gt  gt  2020-05-21 08 28 26 984948 02 00    Initial Aware Datetime and Reconverted Aware Datetime are equal print aware datetime1    aware datetime2   gt  gt  True

User · Answer

Use dateutil tz tzlocal   to get the timezone in your usage of datetime datetime now   and datetime datetime astimezone     from datetime import datetime from dateutil import tz  unlocalisedDatetime   datetime now    localisedDatetime1   datetime now tz   tz tzlocal    localisedDatetime2   datetime 2017  6  24  12  24  36  tz tzlocal    localisedDatetime3   unlocalisedDatetime astimezone tz   tz tzlocal    localisedDatetime4   unlocalisedDatetime replace tzinfo   tz tzlocal      Note that datetime astimezone will first convert your datetime object to UTC then into the timezone  which is the same as calling datetime replace with the original timezone information being None

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In general  to make a naive datetime timezone-aware  use the localize method   import datetime import pytz  unaware   datetime datetime 2011  8  15  8  15  12  0  aware   datetime datetime 2011  8  15  8  15  12  0  pytz UTC   now aware   pytz utc localize unaware  assert aware    now aware   For the UTC timezone  it is not really necessary to use localize since there is no daylight savings time calculation to handle   now aware   unaware replace tzinfo pytz UTC    works    replace returns a new datetime  it does not modify unaware

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Python 3 9 adds the zoneinfo module so now only the standard library is needed  from zoneinfo import ZoneInfo from datetime import datetime unaware   datetime 2020  10  31  12   Attach a timezone   gt  gt  gt  unaware replace tzinfo ZoneInfo  Asia Tokyo    datetime datetime 2020  10  31  12  0  tzinfo zoneinfo ZoneInfo key  Asia Tokyo     gt  gt  gt  str     2020-10-31 12 00 00 09 00   Attach the system s local timezone   gt  gt  gt  unaware replace tzinfo ZoneInfo  localtime    datetime datetime 2020  10  31  12  0  tzinfo zoneinfo ZoneInfo key  localtime     gt  gt  gt  str     2020-10-31 12 00 00 01 00   Subsequently it is properly converted to other timezones   gt  gt  gt  unaware replace tzinfo ZoneInfo  localtime    astimezone ZoneInfo  Asia Tokyo    datetime datetime 2020  10  31  20  0  tzinfo backports zoneinfo ZoneInfo key  Asia Tokyo     gt  gt  gt  str     2020-10-31 20 00 00 09 00   Wikipedia list of available time zones  Windows has no system time zone database  so here an extra package is needed  pip install tzdata     There is a backport to allow use of zoneinfo in Python 3 6 to 3 8  pip install backports zoneinfo  Then  from backports zoneinfo import ZoneInfo

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In the format of unutbu s answer  I made a utility module that handles things like this  with more intuitive syntax  Can be installed with pip   import datetime import saturn  unaware   datetime datetime 2011  8  15  8  15  12  0  now aware   saturn fix naive unaware   now aware madrid   saturn fix naive unaware   Europe Madrid

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I agree with the previous answers  and is fine if you are ok to start in UTC  But I think it is also a common scenario for people to work with a tz aware value that has a datetime that has a non UTC local timezone   If you were to just go by name  one would probably infer replace   will be applicable and produce the right datetime aware object   This is not the case   the replace  tzinfo       seems to be random in its behaviour   It is therefore useless  Do not use this   localize is the correct function to use  Example   localdatetime aware   tz localize datetime nonaware    Or a more complete example   import pytz from datetime import datetime pytz timezone  Australia Melbourne   localize datetime now      gives me a timezone aware datetime value of the current local time   datetime datetime 2017  11  3  7  44  51  908574  tzinfo  lt DstTzInfo  Australia Melbourne  AEDT 11 00 00 DST gt

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I use this statement in Django to convert an unaware time to an aware   from django utils import timezone  dt aware   timezone make aware dt unaware  timezone get current timezone

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All of these examples use an external module  but you can achieve the same result using just the datetime module  as also presented in this SO answer   from datetime import datetime from datetime import timezone  dt   datetime now   dt replace tzinfo timezone utc   print dt replace tzinfo timezone utc  isoformat     2017-01-12T22 11 31 00 00    Fewer dependencies and no pytz issues   NOTE  If you wish to use this with python3 and python2  you can use this as well for the timezone import  hardcoded for UTC    try      from datetime import timezone     utc   timezone utc except ImportError       Hi there python2 user     class UTC tzinfo           def utcoffset self  dt               return timedelta 0          def tzname self  dt               return  UTC          def dst self  dt               return timedelta 0      utc   UTC

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quite new to Python and I encountered the same issue  I find this solution quite simple and for me it works fine  Python 3 6    unaware parser parse  2020-05-01 0 00 00   aware unaware replace tzinfo tz tzlocal    astimezone tz tzlocal

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Here is a simple solution to minimize changes to your code  from datetime import datetime import pytz  start utc   datetime utcnow   print   quot Time  UTC    s quot    start utc strftime  quot  d- m- Y  H  M  S quot      Time  UTC   09-01-2021 03 49 03  tz   pytz timezone  Africa Cairo   start tz   datetime now   astimezone tz  print   quot Time  RSA    s quot    start tz strftime  quot  d- m- Y  H  M  S quot      Time  RSA   09-01-2021 05 49 03

User · Answer

I wrote this at Nov 22 2011   is Pyhton 2 only   never checked if it work on Python 3 I had use from dt aware to dt unaware dt unaware   dt aware replace tzinfo None   and dt unware to dt aware from pytz import timezone localtz   timezone  Europe Lisbon   dt aware   localtz localize dt unware   but answer before is also a good solution

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This codifies  S  rgio and  unutbu s answers  It will  just work  with either a pytz timezone object or an IANA Time Zone string   def make tz aware dt  tz  UTC   is dst None          Add timezone information to a datetime object  only if it is naive         tz   dt tzinfo or tz     try          tz   pytz timezone tz      except AttributeError          pass     return tz localize dt  is dst is dst     This seems like what datetime localize    or  inform   or  awarify    should do  accept both strings and timezone objects for the tz argument and default to UTC if no time zone is specified

[python] How to make an unaware datetime timezone aware in python

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