def _leftmost_descendants(node):
    try:
        treepos = node.treepositions()
    except AttributeError:
        return []
    return [node[x] for x in treepos[1:] if all(y == 0 for y in x)]
Returns the set of all nodes descended in some way through
dataset/ETHPy150Open nltk/nltk/nltk/tgrep.py/_leftmost_descendants