Can't compare naive and aware datetime.now() <= challenge.datetime_end

I am trying to compare the current date and time with dates and times specified in models using comparison operators:

if challenge.datetime_start <= datetime.now() <= challenge.datetime_end:

The script errors out with:

TypeError: can't compare offset-naive and offset-aware datetimes

The models look like this:

class Fundraising_Challenge(models.Model):
    name = models.CharField(max_length=100)
    datetime_start = models.DateTimeField()
    datetime_end = models.DateTimeField()

I also have django using locale date and times.

What I haven't been able to find is the format django uses for DateTimeField(). Is it naive or aware? And how do I get datetime.now() to recognize locale datetime?

Solution 1:

By default, the datetime object is naive in Python, so you need to make both of them either naive or aware datetime objects. This can be done using:

import datetime
import pytz

utc=pytz.UTC

challenge.datetime_start = utc.localize(challenge.datetime_start) 
challenge.datetime_end = utc.localize(challenge.datetime_end) 
# now both the datetime objects are aware, and you can compare them

Note: This would raise a ValueError if tzinfo is already set. If you are not sure about that, just use

start_time = challenge.datetime_start.replace(tzinfo=utc)
end_time = challenge.datetime_end.replace(tzinfo=utc)

BTW, you could format a UNIX timestamp in datetime.datetime object with timezone info as following

d = datetime.datetime.utcfromtimestamp(int(unix_timestamp))
d_with_tz = datetime.datetime(
    year=d.year,
    month=d.month,
    day=d.day,
    hour=d.hour,
    minute=d.minute,
    second=d.second,
    tzinfo=pytz.UTC)

Solution 2:

datetime.datetime.now is not timezone aware.

Django comes with a helper for this, which requires pytz

from django.utils import timezone
now = timezone.now()

You should be able to compare now to challenge.datetime_start

Solution 3:

One line of code solution

if timezone_aware_var <= datetime.datetime.now(timezone_aware_var.tzinfo):
    pass #some code

Explained version

# Timezone info of your timezone aware variable
timezone = your_timezone_aware_variable.tzinfo

# Current datetime for the timezone of your variable
now_in_timezone = datetime.datetime.now(timezone)

# Now you can do a fair comparison, both datetime variables have the same time zone
if your_timezone_aware_variable <= now_in_timezone:
    pass #some code

Summary

You must add the timezone info to your now() datetime.
However, you must add the same timezone of the reference variable; that is why I first read the tzinfo attribute.

Solution 4:

Disable time zone. Use challenge.datetime_start.replace(tzinfo=None);

You can also use replace(tzinfo=None) for other datetime.

if challenge.datetime_start.replace(tzinfo=None) <= datetime.now().replace(tzinfo=None) <= challenge.datetime_end.replace(tzinfo=None):