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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 _adjust_parent_stack(fsh, prev, parents):
 """ Adjust the parent stack in-place as the trigger level changes. Parameters fsh : :class:`FoldScopeHelper` The :class:`FoldScopeHelper` object to act on. prev : :class:`FoldScopeHelper` The previous :class:`FoldScopeHelper` object. parents : list of :class:`FoldScopeHelper` The current list of parent objects. Returns ------- None """

    if prev is None:
        return

    if fsh.fold_scope.trigger_level < prev.fold_scope.trigger_level:
        diff = prev.fold_scope.trigger_level - fsh.fold_scope.trigger_level
        del parents[-diff:]
    elif fsh.fold_scope.trigger_level > prev.fold_scope.trigger_level:
        parents.append(prev)
    elif fsh.fold_scope.trigger_level == prev.fold_scope.trigger_level:
        pass