def get_left_child(self, n):
        '''
        API: get_left_child(self, n)
        Description:
            Returns left child of node n. n can be Node() instance or string
            (name of node).
        Pre:
            Node n should be present in the tree.
        Input:
            n: Node name or Node() instance.
        Return:
            Returns name of the left child of n.
        '''
        if isinstance(n, Node):
            return n.get_attr('Lchild')
        return self.get_node_attr(n, 'Lchild')