code: def overlapping_in_bed( fname, r_chr, r_start, r_stop ):
      
      rval = []
      for line in open( fname ):
          if line.startswith( "#" ) or line.startswith( "track" ):
              continue
          fields = line.split()
          chr, start, stop = fields[0], int( fields[1] ), int( fields[2] )
          if chr == r_chr and start < r_stop and stop >= r_start:
              rval.append( ( chr, max( start, r_start ), min( stop, r_stop ) ) )
      return rval
docs: Get from a bed all intervals that overlap the region defined by
      r_chr, r_start, r_stop.