Can t subtract offset-naive and offset-aware datetimes

Question

I have a timezone aware timestamptz field in PostgreSQL  When I pull data from the table  I then want to subtract the time right now so I can get it s age   The problem I m having is that both datetime datetime now   and datetime datetime utcnow   seem to return timezone unaware timestamps  which results in me getting this error   TypeError  can t subtract offset-naive and offset-aware datetimes    Is there a way to avoid this  preferably without a third-party module being used    EDIT  Thanks for the suggestions  however trying to adjust the timezone seems to give me errors   so I m just going to use timezone unaware timestamps in PG and always insert using   NOW   AT TIME ZONE  UTC    That way all my timestamps are UTC by default  even though it s more annoying to do this

User · Answer

I also faced the same problem  Then I found a solution after a lot of searching    The problem was that when we get the datetime object from model or form it is offset aware and if we get the time by system it is offset naive   So what I did is I got the current time using timezone now   and import the timezone by from django utils import timezone and put the USE TZ   True in your project settings file

User · Answer

This is a very simple and clear solutionTwo lines of code    First we obtain de timezone info o some datatime variable      tz info   your timezone aware variable tzinfo    Now we can subtract two variables using the same time zone info   For instance   Lets obtain the Now   datetime but for the tz info we got before  diff   datetime datetime now tz info -your timezone aware variable   Conclusion  You must mange your datetime variables with the same time info

User · Answer

I came up with an ultra-simple solution   import datetime  def calcEpochSec dt       epochZero   datetime datetime 1970 1 1 tzinfo   dt tzinfo      return  dt - epochZero  total seconds     It works with both timezone-aware and timezone-naive datetime values   And no additional libraries or database workarounds are required

User · Answer

have you tried to remove the timezone awareness  from http   pytz sourceforge net  naive   dt replace tzinfo None   may have to add time zone conversion as well  edit  Please be aware the age of this answer  An answer involving ADDing the timezone info instead of removing it in python 3 is below  https   stackoverflow com a 25662061 93380

User · Answer

I ve found timezone make aware datetime datetime now    is helpful in django  I m on 1 9 1   Unfortunately you can t simply make a datetime object offset-aware  then timetz   it  You have to make a datetime and make comparisons based on that

User · Answer

Is there some pressing reason why you can t handle the age calculation in  PostgreSQL itself  Something like  select    age timeStampField  as timeStampAge from myTable

User · Answer

The correct solution is to add the timezone info e g   to get the current time as an aware datetime object in Python 3   from datetime import datetime  timezone  now   datetime now timezone utc    On older Python versions  you could define the utc tzinfo object yourself  example from datetime docs    from datetime import tzinfo  timedelta  datetime  ZERO   timedelta 0   class UTC tzinfo     def utcoffset self  dt       return ZERO   def tzname self  dt       return  UTC    def dst self  dt       return ZERO  utc   UTC     then   now   datetime now utc

User · Answer

I know some people use Django specifically as an interface to abstract this type of database interaction   Django provides utilities that can be used for this   from django utils import timezone now aware   timezone now     You do need to set up a basic Django settings infrastructure  even if you are just using this type of interface  in settings  you need to include USE TZ True to get an aware datetime    By itself  this is probably nowhere near enough to motivate you to use Django as an interface  but there are many other perks   On the other hand  if you stumbled here because you were mangling your Django app  as I did   then perhaps this helps

User · Answer

I know this is old  but just thought I would add my solution just in case someone finds it useful   I wanted to compare the local naive datetime with an aware datetime from a timeserver  I basically created a new naive datetime object using the aware datetime object  It s a bit of a hack and doesn t look very pretty but gets the job done   import ntplib import datetime from datetime import timezone  def utc to local utc dt       return utc dt replace tzinfo timezone utc  astimezone tz None       try      ntpt   ntplib NTPClient       response   ntpt request  pool ntp org       date   utc to local datetime datetime utcfromtimestamp response tx time       sysdate   datetime datetime now        here comes the fudge         temp date   datetime datetime int str date   4   int str date  5 7   int str date  8 10   int str date  11 13   int str date  14 16   int str date  17 19        dt delta   temp date-sysdate except Exception      print  Something went wrong  -

User · Answer

You don t need anything outside the std libs datetime datetime now   astimezone    If you just replace the timezone it will not adjust the time  If your system is already UTC then  replace tz  UTC   is fine   gt  gt  gt  x datetime datetime now   datetime datetime 2020  11  16  7  57  5  364576    gt  gt  gt  print x  2020-11-16 07 57 05 364576   gt  gt  gt  print x astimezone     2020-11-16 07 57 05 364576-07 00   gt  gt  gt  print x replace tzinfo datetime timezone utc     wrong 2020-11-16 07 57 05 364576 00 00

User · Answer

The psycopg2 module has its own timezone definitions  so I ended up writing my own wrapper around utcnow   def pg utcnow        import psycopg2     return datetime utcnow   replace          tzinfo psycopg2 tz FixedOffsetTimezone offset 0  name None     and just use pg utcnow whenever you need the current time to compare against a PostgreSQL timestamptz

[python] Can't subtract offset-naive and offset-aware datetimes

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