I have this but when I update my module it appends the same tuple

class account_journal_inherit(osv.osv):
 
    _inherit='account.journal'

    def __init__(self, pool, cr):
            
            _type=super(account_journal_inherit, self)._columns['type'].selection
            _type.append(('credit_payment', 'Prepaid Credit'))
            
            return super(account_journal_inherit, self).__init__(pool,cr)

Thanks