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