code: def offset(self, date, n_days):
          '''
          Return the date n_days after (or before if n_days < 0) <date>
          note: not calender days, but self days!
          '''
  #CONSIDER: raise an exception if a date is not in self
          index = self.index(date) + n_days
          if index < 0:
              index = 0
          if index > len(self) - 1:
              index = len(self) - 1
          return self[indexf offset(self, date, n_days):
          '''
          Return the date n_days after (or before if n_days < 0) <date>
          note: not calender days, but self days!
          '''
  #CONSIDER: raise an exception if a date is not in self
          index = self.index(date) + n_days
          if index < 0:
              index = 0
          if index > len(self) - 1:
              index = len(self) - 1
          return self[index]
docs: Return the date n_days after (or before if n_days < 0) <date>
          note: not calender days, but self days!