code: def del_node(self, n):
          '''
          API: del_node(self, n)
          Description:
              Removes node n from tree.
          Pre:
              Node n should be present in the tree.
          Input:
              n: Node name.
          '''
          parent = self.get_node_attr(n, 'parent')
          if self.get_node_attr(n, 'direction') == 'R':
              self.set_node_attr(parent, 'Rchild', None)
          else:
              self.set_node_attr(parent, 'Lchild', None)
          Graph.del_node(self, nf del_node(self, n):
          '''
          API: del_node(self, n)
          Description:
              Removes node n from tree.
          Pre:
              Node n should be present in the tree.
          Input:
              n: Node name.
          '''
          parent = self.get_node_attr(n, 'parent')
          if self.get_node_attr(n, 'direction') == 'R':
              self.set_node_attr(parent, 'Rchild', None)
          else:
              self.set_node_attr(parent, 'Lchild', None)
          Graph.del_node(self, n)
docs: API: del_node(self, n)
          Description:
              Removes node n from tree.
          Pre:
              Node n should be present in the tree.
          Input:
              n: Node name.