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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 register_queryset(self, queryset, validator=None, default=False):
 """ Add a given queryset to the iterator with custom logic for iteration. :param queryset: List of objects included in the reading list. :param validator: Custom logic to determine a queryset's position in a reading_list. Validators must accept an index as an argument and return a truthy value. :param default: Sets the given queryset as the primary queryset when no validator applies. """

        if default or self.default_queryset is None:
            self.default_queryset = queryset
            return
        if validator:
            self.querysets[validator] = queryset
        else:
            raise ValueError(
                """Querysets require validation logic to integrate with reading lists."""
            )