How to solve the strptime() caused naive datetime RuntimeWarning?

Question

I am trying to code without throwing any warnings in my console. So far I have been pretty good at avoiding it until this one case, which seems like a chicken and egg situation to me.

from datetime import datetime as dt 

last_contacted = "19/01/2013"
current_tz = timezone.get_current_timezone()
date_time = dt.strptime(last_contacted, get_current_date_input_format(request))
date_time = current_tz.localize(date_time)

The third line is throwing this warning:

RuntimeWarning: DateTimeField received a naive datetime (2013-01-19 00:00:00) while time zone support is active.)

Its kind of odd, since I need to convert the unicode into a datetime first before I can convert the datetime object into an datetime-aware object (with timezone support) in the forth line.

Any suggestions from experts?

Thanks

UPDATE:

def get_current_date_input_format(request):
    if request.LANGUAGE_CODE == 'en-gb':
        return formats_en_GB.DATE_INPUT_FORMATS[0]
    elif request.LANGUAGE_CODE == 'en':        
        return formats_en.DATE_INPUT_FORMATS[0]

need to see the source of your get_current_date_input_format function as well... — Mike Fogel
This RuntimeWarning only occurs when you assign naive datetime objects to Model instances, so your example code shown shouldn't give this warning unless get_current_date_input_format is doing something special. — Austin Phillips
Thanks, I have updated the question with the requested information. I have noticed if I combine line 3 and line 4, I won't get the warning at all. How strange.. — Houman

Austin Phillips Austin Phillips · Accepted Answer · 2013-01-29T12:45:44

From the comments to your question I am guessing that what you really have in your code is something like this:

from datetime import datetime as dt 

last_contacted = "19/01/2013"
current_tz = timezone.get_current_timezone()
model_instance.date_time = dt.strptime(last_contacted, get_current_date_input_format(request))
model_instance.date_time = current_tz.localize(date_time)

where model_instance is an instance of a Model which has a DateTimeField named date_time.

class MyModel(models.Model)
    ....
    date_time = DateTimeField()

The Python datetime.strptime function returns a naive datetime object which you are attempting to assign to the DateTimeField which is then generating a warning because the use of non-naive datetime objects is incorrect when timezone support is enabled.

If you combine the calls to strptime and localize on a single line, then the complete calculation of converting from a naive datetime to non-naive datetime is done before assigning to date_time and so you won't get an error in this case.

Additional note: Your get_current_date_input_format function should return some default timezone to use in the event that there is no timezone in the request, otherwise the strptime call will fail.

How to solve the strptime() caused naive datetime RuntimeWarning?

2 Answers