code: def get_ids(a):
      
      a_id = '%s.id.fa' % (a.rsplit('.', 1)[0])
      a_id_lookup = '%s.id.lookup' % (a.rsplit('.', 1)[0])
      if check(a_id) is True:
          return a_id, a_id_lookup
      a_id_f = open(a_id, 'w')
      a_id_lookup_f = open(a_id_lookup, 'w')
      ids = []
      for seq in parse_fasta(open(a)):
          id = id_generator() 
          while id in ids:
              id = id_generator() 
          ids.append(id)
          header = seq[0].split('>')[1]
          name = remove_bad(header)
          seq[0] = '>%s %s' % (id, header)
          print('\n'.join(seq), file=a_id_f)
          print('%s\t%s\t%s' % (id, name, header), file=a_id_lookup_f)
      return a_id, a_id_lookup
docs: make copy of sequences with short identifier