def _recurse_leaf_dfs(self, current_node):
    children = self.cluster_tree[(self.cluster_tree['parent'] == current_node)]['child']
    if (len(children) == 0):
        return [current_node]
    else:
        return sum([recurse_leaf_dfs(self.cluster_tree, child) for child in children], [])
def _recurse_leaf_dfs(self, current_node):
    children = self.cluster_tree[(self.cluster_tree['parent'] == current_node)]['child']
    if (len(children) == 0):
        return [current_node]
    else:
        return sum([recurse_leaf_dfs(self.cluster_tree, child) for child in children], [])