from nltk.tree import ParentedTree
import re
traceLeaves = []
line = "( (VP (VBZ says) (SBAR (-NONE- *0*) (S-3 (-NONE- *T*)))))"
currTree = ParentedTree.fromstring(line, remove_empty_top_bracketing = True)
for leaf in currTree.leaves():
if re.search('\*', leaf):
traceLeaves.append(leaf)