code: def _static_folder_path(static_url, static_folder, static_asset):
      
      # first get the asset path relative to the static folder.
      # static_asset is not simply a filename because it could be
      # sub-directory then file etc.
      if not static_asset.startswith(static_folder):
          raise ValueError("%s static asset must be under %s static folder" %
                           (static_asset, static_folder))
      rel_asset = static_asset[len(static_folder):]
      # Now bolt the static url path and the relative asset location together
      return '%s/%s' % (static_url.rstrip('/'), rel_asset.lstrip('/'))
docs: Returns a path to a file based on the static folder, and not on the
      filesystem holding the file.
  
      Returns a path relative to static_url for static_asset