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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 _compute_approver_group_ids(self):
 """Compute the approver groups based on his parents."""

        for page in self:
            res = page.approver_gid
            if page.parent_id:
                res = res | page.parent_id.approver_group_ids
            page.approver_group_ids = res