code: def children(self, node_parent):
          
          
          if node_parent.left is not None:
              yield node_parent.left
          if node_parent.right is not None:
              yield node_parent.right
docs: !
          @brief Returns list of children of node.
          
          @param[in] node_parent (node): Node whose children are required. 
          
          @return (list) Children of node. If node haven't got any child then None is returned.