Get date from ISO week number in Python [duplicate]
%W takes the first Monday to be in week 1 but ISO defines week 1 to contain 4 January. So the result from
datetime.strptime('2011221', '%Y%W%w')is off by one iff the first Monday and 4 January are in different weeks.The latter is the case if 4 January is a Friday, Saturday or Sunday.So the following should work:
from datetime import datetime, timedelta, datedef tofirstdayinisoweek(year, week): ret = datetime.strptime('%04d-%02d-1' % (year, week), '%Y-%W-%w') if date(year, 1, 4).isoweekday() > 4: ret -= timedelta(days=7) return ret