nltk.ImmutableTree.flatten

ImmutableTree.flatten()

Return a flat version of the tree, with all non-root non-terminals removed.

>>> t = Tree.fromstring("(S (NP (D the) (N dog)) (VP (V chased) (NP (D the) (N cat))))")
>>> print(t.flatten())
(S the dog chased the cat)
Returns:a tree consisting of this tree’s root connected directly to its leaves, omitting all intervening non-terminal nodes.
Return type:Tree