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Bob Fang
Bob Fang

Reputation: 7371

Django: How to get a time difference from the time post?

Say I have a class in model

 class Post(models.Model):
     time_posted = models.DateTimeField(auto_now_add=True, blank=True)

     def get_time_diff(self):
         timediff = timediff = datetime.datetime.now() - self.time_posted
         print timediff # this line is never executed
         return timediff

I defined a get_time_diff to get the time difference from the time when the Post is posted up to now, according to the document, the DateTimeField should be able to be converted to datetime automatically, is that correct? Why the print statement is never being run? How can you extract the time difference?

Beside, if you get a time difference, is there an easy way to convert the time difference to an integer, like the number of seconds of the total time.

Upvotes: 31

Views: 37709

Answers (5)

Furkan Siddiqui
Furkan Siddiqui

Reputation: 2015

Simply we can add the custom property to calculate the time difference with the help @property decorator in that model.

from django.utils import timezone


class Post(models.Model):
    time_posted = models.DateTimeField(auto_now_add=True, blank=True)
    content = models.TextField()

    @property
    def time_diff(self):
        return timezone.now() - self.time_posted

time_diff will return object of datetime.timedelta

post = Post.objects.get(pk=1) # Post model object

# time diff in seconds.
post.time_diff.seconds
>>> 652
# time diff in days.
post.time_diff.days
>>> 0

Already answered above nicely by Martijn Pieters, just adding @property, and django.utils.timezone to calculate the difference with respective timezone from settings.py

Upvotes: 0

mr_nobody
mr_nobody

Reputation: 366

Just in case you want to put this process in you Django signals. Here's the one that is working for me. Hope this helps!

from django.db.models.signals import pre_save
from django.dispatch import receiver
from .models import YourModel
from datetime import datetime

@receiver(pre_save, sender = YourModel)
def beforeSave(sender, instance, **kwargs): 
     date_format = "%H:%M:%S"

     # Getting the instances in your model.
     time_start = str(instance.time_start)
     time_end = str(instance.time_end)

     # Now to get the time difference.
     diff = datetime.strptime(time_end, date_format) - datetime.strptime(time_start, date_format)

     # Get the time in hours i.e. 9.60, 8.5
     result = diff.seconds / 3600;

Upvotes: 0

Martijn Pieters
Martijn Pieters

Reputation: 1121266

Your code is already working; a datetime.timedelta object is returned.

To get the total number of seconds instead, you need to call the .total_seconds() method on the resulting timedelta:

from django.utils.timezone import utc

def get_time_diff(self):
    if self.time_posted:
        now = datetime.datetime.utcnow().replace(tzinfo=utc)
        timediff = now - self.time_posted
        return timediff.total_seconds()

.total_seconds() returns a float value, including microseconds.

Note that you need to use a timezone aware datetime object, since the Django DateTimeField handles timezone aware datetime objects as well. See Django Timezones documentation.

Demonstration of .total_seconds() (with naive datetime objects, but the principles are the same):

>>> import datetime
>>> time_posted = datetime.datetime(2013, 3, 31, 12, 55, 10)
>>> timediff = datetime.datetime.now() - time_posted
>>> timediff.total_seconds()
1304529.299168

Because both objects are timezone aware (have a .tzinfo attribute that is not None), calculations between them take care of timezones and subtracting one from the other will do the right thing when it comes to taking into account the timezones of either object.

Upvotes: 43

Wolph
Wolph

Reputation: 80011

Assuming you are doing this within a template, you can also use the timesince template tag.

For example:

{{ blog_date|timesince:comment_date }}

Upvotes: 12

Rohan
Rohan

Reputation: 53316

Your code 

timediff = datetime.datetime.now() - self.pub_date

should work to get the time difference. However, this returns timedelta object. To get difference in seconds you use .seconds attribute

timediff = datetime.datetime.now() - self.pub_date
timediff.seconds  # difference in seconds.

Upvotes: 1

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