code: def _filter_seqs(fn):
      
      out_file = op.splitext(fn)[0] + "_unique.fa"
      idx = 0
      if not file_exists(out_file):
          with open(out_file, 'w') as out_handle:
              with open(fn) as in_handle:
                  for line in in_handle:
                      if line.startswith("@") or line.startswith(">"):
                          fixed_name = _make_unique(line.strip(), idx)
                          seq = in_handle.next().strip()
                          counts = _get_freq(fixed_name)
                          if len(seq) < 26 and (counts > 1 or counts == 0):
                              idx += 1
                              print(fixed_name, file=out_handle, end="\n")
                              print(seq, file=out_handle, end="\n")
                          if line.startswith("@"):
                              in_handle.next()
                              in_handle.next()
      return out_file
docs: Convert names of sequences to unique ids