docs: def fetch_data(dest_dir='.', clobber=False, url=DATA_URL):
      """
      Download data from NCBI required to generate local taxonomy
      database. Default url is ncbi.DATA_URL
  
      * dest_dir - directory in which to save output files (created if necessary).
      * clobber - don't download if False and target of url exists in dest_dir
      * url - url to archive; default is ncbi.DATA_URL
  
      Returns (fname, downloaded), where fname is the name of the
      downloaded zip archive, and downloaded is True if a new files was
      downloaded, false otherwise.
  
      see ftp://ftp.ncbi.nih.gov/pub/taxonomy/taxdump_readme.txt
      """
  
      dest_dir = os.path.abspath(dest_dir)
      try:
          os.mkdir(dest_dir)
      except OSError:
          pass
  
      fout = os.path.join(dest_dir, os.path.split(url)[-1])
  
      if os.access(fout, os.F_OK) and not clobber:
          downloaded = False
          logging.info(fout + ' exists; not downloading')
      else:
          downloaded = True
          logging.info('downloading {} to {}'.format(url, fout))
          request.urlretrieve(url, fout)
  
      return (fout, downloaded)