Select read in bamPEFragment using the conditions below. What is the flag in samtools for the conditions below?

reads = np.array([(abs(r.template_length), r.infer_query_length(always=False))
                          for r in bam.fetch(chrom, start, end)
                          if r.is_proper_pair and r.is_read1 and not r.is_unmapped])