docstr: Set the node label.  This will only succeed the first time the
  node label is set, which should occur in ImmutableTree.__init__().
docstr_tok: ["Set","the","node","label",".","This","will","only","succeed","the","first","time","the","node","label","is","set",",","which","should","occur","in","ImmutableTree.__init__","(",")","."]
code: def set_label(self, value):
      """
      Set the node label.  This will only succeed the first time the
      node label is set, which should occur in ImmutableTree.__init__().
      """
      if hasattr(self, "_label"):
          raise ValueError(
              "%s may not be modified" % type(self).__name__
          )
      self._label = value
  
imports: from nltk.probability import ProbabilisticMixIn
  from nltk.tree.parented import MultiParentedTree, ParentedTree
  from nltk.tree.tree import Tree
label_desc: Use image node_id 15 for calling the ImmutableTree obj's underlying member method code with example usage: obj.set_label(value) without return types