code: def off_to_pos(self, off):
          
          idx = 0
          nb = 0
          for i in self.get_instructions():
              if idx == off:
                  return nb
              nb += 1
              idx += i.get_length()
          return -1
docs: Get the position of an instruction by using the address
  
          :param off: address of the instruction
          :type off: int
  
          :rtype: int