recluze recluze -4 years ago 193
Python Question

How to calculate difference between two dates in weeks in python

I'm trying to calculate the difference between two dates in "weeks of year". I can get the datetime object and get the days etc but not week numbers. I can't, of course, subtract dates because weekends can't be ensured with that.

I tried getting the week number using

d1.isocalendar()[1]
and subtracting
d2.isocalendar()[1]
but the issue is that
isocalendar()[1]
returns
December 31, 2012
as week 1 (which supposedly is correct) but that means my logic cannot span over this date.

For reference, here's my complete code:

def week_no(self):
ents = self.course.courselogentry_set.all().order_by('lecture_date')
l_no = 1
for e in ents:
if l_no == 1:
starting_week_of_year = e.lecture_date.isocalendar()[1] # get week of year
initial_year = e.lecture_date.year
if e == self:
this_year = e.lecture_date.year
offset_week = (this_year - initial_year) * 52
w_no = e.lecture_date.isocalendar()[1] - starting_week_of_year + 1 + offset_week
break
l_no += 1
return w_no


With this code, the lecture on Dec 31, 2012 ends up being -35.

Answer Source

How about calculating the difference in weeks between the Mondays within weeks of respective dates? In the following code, monday1 is the Monday on or before d1 (the same week):

from datetime import datetime, timedelta

monday1 = (d1 - timedelta(days=d1.weekday()))
monday2 = (d2 - timedelta(days=d2.weekday()))

print 'Weeks:', (monday2 - monday1).days / 7

Returns 0 if both dates fall withing one week, 1 if on two consecutive weeks, etc.

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