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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 action_cancel(self):
 """Set a change request as cancelled."""

        self.write({'state': 'cancelled'})
        for rec in self:
            rec.message_post(
                subtype='mt_comment',
                body=_(
                    'Change request <b>%s</b> has been cancelled by %s.'
                    ) % (rec.display_name, self.env.user.name)
                )