<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def execute(self, portfolio_name=None):
 """ Place the order with LendingClub Parameters portfolio_name : string The name of the portfolio to add the invested loan notes to. This can be a new or existing portfolio name. Raises ------ LendingClubError Returns ------- int The completed order ID """

        assert self.order_id == 0, 'This order has already been place. Start a new order.'
        assert len(self.loans) > 0, 'There aren\'t any loans in your order'

        # Place the order
        self.__stage_order()
        token = self.__get_strut_token()
        self.order_id = self.__place_order(token)

        self.__log('Order #{0} was successfully submitted'.format(self.order_id))

        # Assign to portfolio
        if portfolio_name:
            return self.assign_to_portfolio(portfolio_name)

        return self.order_id