code: def get_farthest_leaf(self, topology_only=False, is_leaf_fn=None):
          
          min_node, min_dist, max_node, max_dist = self._get_farthest_and_closest_leaves(
          topology_only=topology_only, is_leaf_fn=is_leaf_fn)
          return max_node, max_dist
docs: Returns node's farthest descendant node (which is always a leaf), and the
          distance to it.
  
          :argument False topology_only: If set to True, distance
            between nodes will be referred to the number of nodes
            between them. In other words, topological distance will be
            used instead of branch length distances.
  
          :return: A tuple containing the farthest leaf referred to the
            current node and the distance to it.