Django relative_time templatetag

relative_time.py

from django import template
from django.template.defaultfilters import pluralize

from datetime import datetime
from dateutil import parser # http://labix.org/python-dateutil
from pytz import timezone # http://pytz.sourceforge.net/
from math import floor
 
register = template.Library()

def to_datetime(string):
	"""
		Convert a string to a datetime
	"""
	try:
		return parser.parse(string)
	except:
		return string
	
register.filter(to_datetime)

def relative_time(obj):
	"""
		Convert datetime objects into relative t
	"""
	dt = to_datetime(obj)
	string = ""
	
	utc = timezone('UTC')
	now = datetime.now(tz = utc)
	diff = float( (now - dt).days * 86400 + (now - dt).seconds )
	if( diff <= 30 * 60 ): # the difference is 30 seconds or less
		string = 'now'
	else:
		string = 'about '
		t = {
			'year': 0,
			'month': 0,
			'week': 0,
			'day': 0,
			'hour': 0,
			'minute': 0,
		}
		t['year']	=	floor( diff / float(31536000) ) # assume 365 days in a year
		t['month']	=	floor( ( diff - ( t['year'] * float(31536000) ) ) / float(2592000) ) # assume a month is 30 days
		t['week']	=	floor( ( diff - ( t['year'] * float(31536000) ) - ( t['month'] * float(2592000) ) ) / float(604800) )
		t['day']	=	floor( ( diff - ( t['year'] * float(31536000) ) - ( t['month'] * float(2592000) ) - ( t['week'] * float(604800) ) ) / float(86400) )
		t['hour']	=	floor( ( diff - ( t['year'] * float(31536000) ) - ( t['month'] * float(2592000) ) - ( t['week'] * float(604800) ) - ( t['day'] * float(86400) ) ) / float(3600) )
		t['minute']	=	round( ( diff - ( t['year'] * float(31536000) ) - ( t['month'] * float(2592000) ) - ( t['week'] * float(604800) ) - ( t['day'] * float(86400) ) - ( t['hour'] * float(3600) ) ) / float(60) )
		for unit in t:
			t[unit] = int(t[unit])

		if t['year']:
			string += u'%d %s, ' % (t['year'], pluralize(t['year'], 'year,years'))
			if t['month']:
				string += u'%d %s, ' % (t['month'], pluralize(t['month'], 'month,months'))
			elif t['week']:
				string += u'%d %s, ' % (t['week'], pluralize(t['week'], 'week,weeks'))
			elif t['day']:
				string += u'%d %s, ' % (t['day'], pluralize(t['day'], 'day,days'))
		elif t['month']:
			string += u'%d %s, ' % (t['month'], pluralize(t['month'], 'month,months'))
			if t['week']:
				string += u'%d %s, ' % (t['week'], pluralize(t['week'], 'week,weeks'))
			elif t['day']:
				string += u'%d %s, ' % (t['day'], pluralize(t['day'], 'day,days'))
		elif t['week']:
			string += u'%d %s, ' % (t['week'], pluralize(t['week'], 'week,weeks'))
			if t['day']:
				string += u'%d %s, ' % (t['day'], pluralize(t['day'], 'day,days'))
		elif t['day']:
			string += u'%d %s, ' % (t['day'], pluralize(t['day'], 'day,days'))
		elif t['hour']:
			string += u'%d %s, ' % (t['hour'], pluralize(t['hour'], 'hour,hours'))
			if t['hour'] < 13 and t['minute']:
				string += u'%d %s, ' % (t['minute'], pluralize(t['minute'], 'minute,minutes'))
		elif t['minute']:
			string += u'%d %s, ' % (t['minute'], pluralize(t['minute'], 'minute,minutes'))
		
		string = string.rstrip(', ') + ' ago'
		string = ' and '.join( string.rsplit(', ') )

	return string
	
register.filter(relative_time)