To set process in subscription module, first you need to install subscription module and set interval number and interval type fields in subscription module is used to set the process. You can use this function as given below

def process(self, cr, uid, ids, context=None):
        for row in self.read(cr, uid, ids, context=context):
            mapping = {'name':'name','interval_number':'interval_number','interval_type':'interval_type','exec_init':'numbercall','date_init':'nextcall'}
            res = {'model':'subscription.subscription', 'args': repr([[row['id']]]), 'function':'model_copy', 'priority':6, 'user_id':row['user_id'] and row['user_id'][0]}
            for key,value in mapping.items():
                res[value] = row[key]
            id = self.pool.get('ir.cron').create(cr, uid, res)
            self.write(cr, uid, [row['id']], {'cron_id':id, 'state':'running'})
        return True