Can't subtract offset-naive and offset-aware datetimes
Solution 1
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
Solution 2
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)
Solution 3
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...
Solution 4
This is a very simple and clear solution
Two 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
Solution 5
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.
>>> x=datetime.datetime.now()
datetime.datetime(2020, 11, 16, 7, 57, 5, 364576)
>>> print(x)
2020-11-16 07:57:05.364576
>>> print(x.astimezone())
2020-11-16 07:57:05.364576-07:00
>>> print(x.replace(tzinfo=datetime.timezone.utc)) # wrong
2020-11-16 07:57:05.364576+00:00
Comments
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Ian over 3 years
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()
anddatetime.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).