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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 set_reviewing(self, hit_id, revert=None):
 """ Update a HIT with a status of Reviewable to have a status of Reviewing, or reverts a Reviewing HIT back to the Reviewable status. Only HITs with a status of Reviewable can be updated with a status of Reviewing. Similarly, only Reviewing HITs can be reverted back to a status of Reviewable. """

        params = {'HITId' : hit_id,}
        if revert:
            params['Revert'] = revert
        return self._process_request('SetHITAsReviewing', params)