docs: def todo_lists(self, project_id, complete=None):
          """
          This will return the metadata for all of the lists in a given project.
          You can further constrain the query to only return those lists that
          are "complete" (have no uncompleted items) or "uncomplete" (have
          uncompleted items remaining).
          """
          path = '/projects/%u/todos/lists' % project_id
          req = ET.Element('request')
          if complete is not None:
              ET.SubElement(req, 'complete').text = str(bool(complete)).lower()
          return self._request(path, req)