code: def set(self, quote_id, customer_data, store_view=None):
          
          return bool(
              self.call('cart_customer.set',
                  [quote_id, customer_data, store_view])
          )
docs: Add customer information into a shopping cart
  
          :param quote_id: Shopping cart ID (quote ID)
          :param customer_data, dict of customer details, example
              {
                  'firstname': 'testFirstname',
                  'lastname': 'testLastName',
                  'email': 'testEmail',
                  'website_id': '0',
                  'store_id': '0',
                  'mode': 'guest'
              }
          :param store_view: Store view ID or code
          :return: boolean, True if information added