docs: def get_books_for_schedule(self, schedule):
          """
          Returns a dictionary of data.  SLNs are the keys, an array of Book
          objects are the values.
          """
          slns = self._get_slns(schedule)
  
          books = {}
  
          for sln in slns:
              try:
                  section_books = self.get_books_by_quarter_sln(
                      schedule.term.quarter, sln
                  )
                  books[sln] = section_books
              except DataFailureException:
                  # do nothing if bookstore doesn't have sln
                  pass
          return books