code: def _start_date_of_year(year: int) -> datetime.date:
      
  
      jan_one = datetime.date(year, 1, 1)
      diff = 7 * (jan_one.isoweekday() > 3) - jan_one.isoweekday()
  
      return jan_one + datetime.timedelta(days=diff)
docs: Return start date of the year using MMWR week rules