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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 page_index(self, page_index):
 """ Sets the page_index of this V1Page. The page's position in the merchant's list of pages. Always an integer between 0 and 6, inclusive. :param page_index: The page_index of this V1Page. :type: int """


        if page_index is None:
            raise ValueError("Invalid value for `page_index`, must not be `None`")
        if page_index > 6:
            raise ValueError("Invalid value for `page_index`, must be a value less than or equal to `6`")
        if page_index < 0:
            raise ValueError("Invalid value for `page_index`, must be a value greater than or equal to `0`")

        self._page_index = page_index