code: def _iso_year_start(iso_year):
      "The gregorian calendar date of the first day of the given ISO year"
      fourth_jan = dt.date(iso_year, 1, 4)
      delta = dt.timedelta(fourth_jan.isoweekday()-1)
      return fourth_jan - deltf _iso_year_start(iso_year):
      "The gregorian calendar date of the first day of the given ISO year"
      fourth_jan = dt.date(iso_year, 1, 4)
      delta = dt.timedelta(fourth_jan.isoweekday()-1)
      return fourth_jan - delta
docs: The gregorian calendar date of the first day of the given ISO year