code: def _read_geneset(self, study_fn, pop_fn):
          
          pop = set(_.strip() for _ in open(pop_fn) if _.strip())
          study = frozenset(_.strip() for _ in open(study_fn) if _.strip())
          if next(iter(pop)).isdigit():
              pop = set(int(g) for g in pop)
              study = frozenset(int(g) for g in study)
          # some times the pop is a second group to compare, rather than the
          # population in that case, we need to make sure the overlapping terms
          # are removed first
          if self.args.compare:
              common = pop & study
              pop |= study
              pop -= common
              study -= common
              sys.stderr.write("removed %d overlapping items\n" % (len(common)))
              sys.stderr.write("Set 1: {0}, Set 2: {1}\n".format(
                  len(study), len(pop)))
          return study, pop
docs: Open files containing genes. Return study genes and population genes.