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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 start_index(self):
 """Return the 1-based index of the first item on this page."""

        paginator = self.paginator
        # Special case, return zero if no items.
        if paginator.count == 0:
            return 0
        elif self.number == 1:
            return 1
        return (
            (self.number - 2) * paginator.per_page + paginator.first_page + 1)