Django - Time since model created

Question

How du you calculate the time since a model was created? The model has the following field:

created_at = models.DateTimeField(auto_now_add=True)

This is what I tried:

from datetime import datetime, timedelta

@property
def time_since_created(self):
    return (datetime.now()-self.created_at).total_seconds()

What I do not understand is that it crashes without giving me any error messages. If I wrap it in a try/except block like this:

@property
    def time_since_created(self):
        try:
            return (datetime.now()-self.created_at).total_seconds()
        except Exception as e:
            try:
                print("Error:" + e)
            except:
                print("Error: An exception occured when trying to print exception")

The error I will get is "Error: An exception occured when trying to print exception". If I do not include the last try/catch block I won't get any output at all.

Do anyone have any ideas?

Can you elaborate on what did not work? error message? wrong result? — bakkal, Jun 27 '15 at 18:15
is `time_since_created` a method inside the model's class? I see only the function but no class so I am not sure — bakkal, Jun 27 '15 at 18:55
Yes it is, I use it in a serializer class in django rest framework. — Valdemar Edvard Sandal Rolfsen, Jun 27 '15 at 18:59
Try `print(e)` or `print('Error': + str(e))` see what message you get from the first exception (if you're going to concatenate the string I think you need to convert `str(e)`) — bakkal, Jun 27 '15 at 19:05
Are you using `USE_TZ` setting in your project? What is its value? — bellum, Jun 27 '15 at 20:21
Yes but what is the error? You should be able to read the exception message — bakkal, Jun 27 '15 at 22:28
@bakkal I finally got an error message. It said Error:can't subtract offset-naive and offset-aware datetimes — Valdemar Edvard Sandal Rolfsen, Jun 28 '15 at 10:26

score 2 · Accepted Answer · answered Jun 28 '15 at 05:59

2

I have tried to do the same actions by myself and I have got error:

can't subtract offset-naive and offset-aware datetimes

It's because datetime.now() is naive and self.created_at is aware time. So try to use timezone.now() instead:

from django.utils import timezone

@property
def time_since_created(self):
    return (timezone.now()-self.created_at).total_seconds()

answered Jun 28 '15 at 05:59

bellum

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I'm adding dateTime to `time_since_created(dateTime)`. But it gives me this error: **'property' object is not callable** – AnonymousUser Jun 08 '22 at 07:37

score -2 · Answer 2 · edited May 23 '17 at 11:58

Edit: re-post for django solution

After checking previous stackoverflow post here and some other post. They suggest not to using the auto_now_add, but add default argument as format.

created_date = models.DateTimeField(default=datetime.now())

I think it might be the format problem, and this should solve that. And sorry for my previous answer.

Edit: after checking the django source code here, the auto_now_add arg appear to apply

value = datetime.datetime.now().time()

to model instance.

And in my test, if I "minus" this value with datetime.now().time(), it pops

TypeError: unsupported operaand type(s) for -: 'datetime.datetime' and 'datetime.time'

But I'm not sure about your django version, maybe the source code has been modified.

didn't notice this is a django question, my apologies. – Jkm Jun 27 '15 at 18:50 — Jkm, Jun 27 '15 at 18:50

Django - Time since model created

2 Answers2