code: def filter_single_reads_by_length(in_file, quality_format, min_length=20,
                                    out_file=None):
      
      logger.info("Removing reads in %s thare are less than %d bases."
                  % (in_file, min_length))
      in_iterator = SeqIO.parse(in_file, quality_format)
      out_iterator = (record for record in in_iterator if
                      len(record.seq) > min_length)
      with file_transaction(out_file) as tmp_out_file:
          with open(tmp_out_file, "w") as out_handle:
              SeqIO.write(out_iterator, out_handle, quality_format)
      return out_file
docs: removes reads from a fastq file which are shorter than a minimum
      length