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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _unset_child(self, name, child):
 """ Untie child from parent. :param name: Child name. :param child: Parentable object. """

        if name not in self._children or self._children[name] is not child:
            msg = 'Child {child} with name "{name}" is not found'
            raise ValueError(msg.format(child=child, name=name))
        child._set_parent(None)
        self._remove_child(name, child)