Django - Time since model created

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?