code: def _known_populations(row, pops):
      
      cutoff = 0.01
      out = set([])
      for pop, base in [("esp", "af_esp_all"), ("1000g", "af_1kg_all"),
                        ("exac", "af_exac_all"), ("anypop", "max_aaf_all")]:
          for key in [x for x in pops if x.startswith(base)]:
              val = row[key]
              if val and val > cutoff:
                  out.add(pop)
      return sorted(list(out))
docs: Find variants present in substantial frequency in population databases.