[Zope-dev] PythonScript for iso_week

[Steve Alexander]

Hi folks,

At various times in the past, people on this list have asked about 
getting week numbers from DateTime instances.

I recently had this requirement, so I wrote a PythonScript to produce an 
iso_week tuple (year, week_number, dow_monday_is_one__sunday_is_seven) 
from a DateTime instance.

I've submitted the same to the collector as a feature-enhancement patch 
to DateTime.py.

I've tested this by empirically comparing it with the output of 
mxDateTime's iso_week attribute for all days from 1920-01-01 to some 
date in the twenty-third century.

Note also that this iso_week method does not create additional DateTime 
instances.

See also http://www.cl.cam.ac.uk/~mgk25/iso-time.html

--------
PythonScript iso_week

Parameters: date

doy=date.dayOfYear()
dow=(date.dow()-1)%7
y=date.year()
thurs_this_week=doy+(3-dow)
is_leap=y%4==0 and (y%100!=0 or y%400==0)

if thurs_this_week>(is_leap and 366 or 365):
   week=1
   if dow<8:
     y=y+1
else:
   mon_this_week=doy-dow
   day_year_begins=(dow-doy+1)%7
   day_of_4_jan=(day_year_begins+3)%7
   monday_of_first_week=4-day_of_4_jan
   week=(mon_this_week-monday_of_first_week)/7+1

   if week==0:
     y=y-1
     is_last_leap=y%4==0 and (y%100!=0 or y%400==0)
     if day_year_begins==4 or (day_year_begins==5 and is_last_leap):
       week=53
     else:
       week=52

return y,week,dow+1
--------


--
Steve Alexander
Software Engineer
Cat-Box limited
http://www.cat-box.net