class_docstr: A ``Tree`` that automatically maintains parent pointers for
  single-parented trees.  The following are methods for querying
  the structure of a parented tree: ``parent``, ``parent_index``,
  ``left_sibling``, ``right_sibling``, ``root``, ``treeposition``.
  
  Each ``ParentedTree`` may have at most one parent.  In
  particular, subtrees may not be shared.  Any attempt to reuse a
  single ``ParentedTree`` as a child of more than one parent (or
  as multiple children of the same parent) will cause a
  ``ValueError`` exception to be raised.
  
  ``ParentedTrees`` should never be used in the same tree as ``Trees``
  or ``MultiParentedTrees``.  Mixing tree implementations may result
  in incorrect parent pointers and in ``TypeError`` exceptions.
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code: def _delparent(self, child, index):
      # Sanity checks
      assert isinstance(child, ParentedTree)
      assert self[index] is child
      assert child._parent is self
  
      # Delete child's parent pointer.
      child._parent = None
  
imports: import warnings
  from abc import ABCMeta, abstractmethod
  from nltk.tree.tree import Tree
  from nltk.util import slice_bounds
label_desc: Use image node_id 10 for calling the ParentedTree obj's underlying member method code with example usage: obj._delparent(child, index) without return types