Python is via datetime.isocalendar() able to produce the ISO week number and ISO weekday from a given date. But it is not possible to do the reverse; calculate the date from a year, ISO week number and weekday.

libc strptime()/strftime() mentions a %V and %u directive which does this, i.e. Monday in ISO week 22 of the year 2011:

   datetime.strptime('2011221', '%Y%V%u')

returning 2011-05-30 and

   datetime.strptime('2011227', '%Y%V%u')

returning 2011-06-05


libc (on FreeBSD) has this to say:

%V is replaced by the week number of the year (Monday as the first day
   of the week) as a decimal number (01-53).  If the week containing
   January 1 has four or more days in the new year, then it is week 1;
   otherwise it is the last week of the previous year, and the next
   week is week 1.

%u is replaced by the weekday (Monday as the first day of the week) as
   a decimal number (1-7).