human
Complete this python program:
def _postorder_traverse(root, get_children):
assistant
#Here is the Python program you requested.

    """Traverse a tree in depth-first post-order (children before parent).
    """
    def dfs(elem):
        for v in get_children(elem):
            for u in dfs(v):
                (yield u)
        (yield elem)
    for elem in dfs(root):
        (yield elem)