code: def namespace_uri(self, name):
          
          a_node = self.adapter.get_node_attribute_node(self.impl_element, name)
          if a_node is None:
              return None
          return self.adapter.get_node_namespace_uri(a_node)
docs: :param string name: the name of an attribute to look up.
  
          :return: the namespace URI associated with the named attribute,
              or None.