code: def get_cache_buster(src_path, method='importtime'):
      
      try:
          fn = _BUST_METHODS[method]
      except KeyError:
          raise KeyError('Unsupported busting method value: %s' % method)
  
      return fn(src_path)
docs: Return a string that can be used as a parameter for cache-busting URLs
      for this asset.
  
      :param src_path:
          Filesystem path to the file we're generating a cache-busting value for.
  
      :param method:
          Method for cache-busting. Supported values: importtime, mtime, md5
          The default is 'importtime', because it requires the least processing.
  
      Note that the mtime and md5 cache busting methods' results are cached on
      the src_path.
  
      Example::
  
          >>> SRC_PATH = os.path.join(os.path.dirname(__file__), 'html.py')
          >>> get_cache_buster(SRC_PATH) is _IMPORT_TIME
          True
          >>> get_cache_buster(SRC_PATH, method='mtime') == _cache_key_by_mtime(SRC_PATH)
          True
          >>> get_cache_buster(SRC_PATH, method='md5') == _cache_key_by_md5(SRC_PATH)
          True