code: def parse(self, limit=None):
          
          if limit is not None:
              LOG.info("Only parsing first %s rows fo each file", str(limit))
  
          LOG.info("Parsing files...")
  
          if self.test_only:
              self.test_mode = True
  
          self._process_diseases(limit)
          self._process_genes(limit)
          self._process_genes_kegg2ncbi(limit)
          self._process_omim2gene(limit)
          self._process_omim2disease(limit)
          self._process_kegg_disease2gene(limit)
  
          self._process_pathways(limit)
          self._process_pathway_pubmed(limit)
          # self._process_pathway_pathway(limit)
          self._process_pathway_disease(limit)
          self._process_pathway_ko(limit)
  
          self._process_ortholog_classes(limit)
          # TODO add in when refactoring for #141
          # for f in ['hsa_orthologs', 'mmu_orthologs', 'rno_orthologs',
          #           'dme_orthologs','dre_orthologs','cel_orthologs']:
          #     file = '/'.join((self.rawdir, self.files[f]['file']))
          #     self._process_orthologs(file, limit)  # DONE #
  
          LOG.info("Finished parsing")
  
          return
docs: :param limit:
          :return: