code: def get_random(self, n, l=None):
          
          random_f = Fasta()
          if l:
              ids = self.ids[:]
              random.shuffle(ids)
              i = 0
              while (i < n) and (len(ids) > 0):
                  seq_id = ids.pop()
                  if (len(self[seq_id]) >= l):
                      start = random.randint(0, len(self[seq_id]) - l)
                      random_f["random%s" % (i + 1)] = self[seq_id][start:start+l]
                      i += 1
              if len(random_f) != n:
                  sys.stderr.write("Not enough sequences of required length")
                  return
              else:
                  return random_f
  
          else:
              choice = random.sample(self.ids, n)
              for i in range(n):
                  random_f[choice[i]] = self[choice[i]]
          return random_f
docs: Return n random sequences from this Fasta object