code: def c14n_uri(sqluri):
      
      uri_c14n_method = _get_methods_by_uri(sqluri)[METHOD_C14N_URI]
      if not uri_c14n_method:
          return sqluri
      return uri_c14n_method(sqluri)
docs: Ask the backend to c14n the uri. See register_uri_backend() for
      details.
  
      If no backend is found for this uri method, a NotImplementedError
      will be raised.