code: def _get_human_models_file(self):
          
  
          base_url = 'ftp.flybase.net'
          human_disease_dir = 'releases/current/precomputed_files/human_disease'
          from ftplib import FTP
          ftp = FTP(base_url)     # connect to host
          ftp.login()
          ftp.cwd(human_disease_dir)
          l = ftp.nlst()          # get list of files
          ftp.quit()
          f = None
          f_list = [
              i for i, x in enumerate(l)
              if re.match(r'allele_human_disease_model', x)]
          if len(f_list) == 0:
              LOG.error("Can't find the human_disease_model file")
          elif len(f_list) > 1:
              LOG.error(
                  "There's >1 human disease model file, " +
                  "and I don't know which to choose: %s", str(l))
          else:
              f = l[f_list[0]]
  
          if f is not None:
              # cat the url together
              file_url = '/'.join(('ftp:/', base_url, human_disease_dir, f))
              self.files['disease_models']['url'] = file_url
  
              # while we're at it, set the version...
              m = re.match(
                  r'allele_human_disease_model_data_fb_(\d+_\d+).tsv.gz', f)
              # allele_human_disease_model_data_fb_2015_03.tsv.gz
              if m:
                  ver = 'FB' + m.group(1)
                  self.version_num = ver
  
          return
docs: This function uses ftp to probe the FTP site to get the name of
          the current human_models file, and sets it in the files object.
          :return: