def get_app_url(config):
  """ Returns the application's URL, based on the given config. """
  return '%s://%s' % (config['PREFERRED_URL_SCHEME'], config['SERVER_HOSTNAME'])

def slash_join(*args):
  """
  Joins together strings and guarantees there is only one '/' in between the
  each string joined. Double slashes ('//') are assumed to be intentional and
  are not deduplicated.
  """
  def rmslash(path):
    path = path[1:] if len(path) > 0 and path[0] == '/' else path
    path = path[:-1] if len(path) > 0 and path[-1] == '/' else path
    return path

  args = [rmslash(path) for path in args]
  return '/'.join(args)