code: def calc_frip(self, input_bam, input_bed, threads=4):
          
          cmd = self.simple_frip(input_bam, input_bed, threads)
          return subprocess.check_output(cmd.split(" "), shell=True)
docs: Calculate fraction of reads in peaks.
  
          A file of with a pool of sequencing reads and a file with peak call
          regions define the operation that will be performed. Thread count
          for samtools can be specified as well.
  
          :param str input_bam: sequencing reads file
          :param str input_bed: file with called peak regions
          :param int threads: number of threads samtools may use
          :return float: fraction of reads in peaks defined in given peaks file