code: def get_knownGene_hg19(self):
          
          if self._knownGene_hg19 is None:
              self._knownGene_hg19 = self._load_knownGene(self._get_path_knownGene_hg19())
  
          return self._knownGene_hg19
docs: Get UCSC knownGene table for Build 37.
  
          Returns
          -------
          pandas.DataFrame
              knownGene table if loading was successful, else None