<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def handle_namespace_url(self, line: str, position: int, tokens: ParseResults) -> ParseResults: """Handle statements like ``DEFINE NAMESPACE X AS URL "Y"``. :raises: RedefinedNamespaceError :raises: pybel.resources.exc.ResourceError """

        namespace = tokens['name']
        self.raise_for_redefined_namespace(line, position, namespace)

        url = tokens['url']
        self.namespace_url_dict[namespace] = url

        if self.skip_validation:
            return tokens

        namespace_result = self.manager.get_or_create_namespace(url)

        if isinstance(namespace_result, dict):
            self.namespace_to_term[namespace] = namespace_result
            self.uncachable_namespaces.add(url)
        else:
            self.namespace_to_term[namespace] = self.manager.get_namespace_encoding(url)

        return tokens