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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 get_reviewable_hits(self, hit_type=None, status='Reviewable', sort_by='Expiration', sort_direction='Ascending', page_size=10, page_number=1):
 """ Retrieve the HITs that have a status of Reviewable, or HITs that have a status of Reviewing, and that belong to the Requester calling the operation. """

        params = {'Status' : status,
                  'SortProperty' : sort_by,
                  'SortDirection' : sort_direction,
                  'PageSize' : page_size,
                  'PageNumber' : page_number}

        # Handle optional hit_type argument
        if hit_type is not None:
            params.update({'HITTypeId': hit_type})

        return self._process_request('GetReviewableHITs', params, [('HIT', HIT),])