NickName:berserkia Ask DateTime:2013-10-18T09:16:39

Save old dates and display time until next anniversary of that date in Django

I'm trying to write a basic reminder app where users can enter important dates (birthdays, anniversaries, etc.) and see how much time is left until the next anniversary of that date. For example, a user can have a birthday as something like Jan 1st 1990, and I want to display for them the time until their next birthday (2 months 14 days).

I've been using the django timeuntil built in template tag, but it only works for dates in the future (it won't display anything if the date is before the current date). I'm not sure how to to go about "normalizing" the entered date to be a time in the future.

Current code:

def events(request):
    relationships = Relationship.objects.filter(user=request.user)
     events = Event.objects.filter(user=request.user).order_by('date')[:8]
    event_date = events[0].date

    if datetime.now() >= event_date:
        difference = datetime.now() - event_date
        event_date_new = event_date + difference
        event_date = event_date_new
     context = {
         'relationships': relationships,
         'events': events
      }
     return render(request, 'app/events.html', context)

Template

<td class="column-right"><h4>{{event.date|timeuntil}}</h4></td>

(It also throws an error on datetime.now() module has no attribute "now", is that an old way to find the current date?)

Thanks in advance!

Copyright Notice：Content Author:「berserkia」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/19440005/save-old-dates-and-display-time-until-next-anniversary-of-that-date-in-django

Answers

Peter DeGlopper 2013-10-18T01:26:58

now is a method of the datetime.datetime class, not the datetime module:\n\ndifference = datetime.datetime.now() - event_date\n\n\nThat said, your correction logic is off. If you write out the calculation in one line, it should be clear why:\n\ndifference = datetime.now() - event_date\nevent_date_new = event_date + difference\n\n\nSo by substitution:\n\nevent_date_new = event_date + (datetime.now() - event_date)\n\n\nWhich simplifies to:\n\nevent_date_new = datetime.now()\n\n\nI would try it this way:\n\nnow = datetime.datetime.now()\nevent_date = event_date.replace(year=now.year)\nif event_date < now:\n event_date.replace(year=now.year + 1)\n\n\nAs Christian Ternus points out, that won't work if event_date is a leap day. You could disallow leap days as event_date values, requiring the user to enter either February 28th or March 1st. Or you could catch the ValueError exception raised by replace and make the correction, adding or subtracting a one-day timedelta. Or use calendar.isleap to figure out the next leap year, if you want to show the true time interval.",