code: def get_slot_positions(self, type='a'):
          
          if type not in ALLOWED_ANALYSES_TYPES and type != ALL_ANALYSES_TYPES:
              return list()
  
          layout = self.getLayout()
          slots = list()
  
          for pos in layout:
              if type != ALL_ANALYSES_TYPES and pos['type'] != type:
                  continue
              slots.append(to_int(pos['position']))
  
          # return a unique list of sorted slot positions
          return sorted(set(slots))
docs: Returns a list with the slots occupied for the type passed in.
  
          Allowed type of analyses are:
  
              'a'   (routine analysis)
              'b'   (blank analysis)
              'c'   (control)
              'd'   (duplicate)
              'all' (all analyses)
  
          :param type: type of the analysis
          :return: list of slot positions