code: def get_symbols_with_positive_balances(self) -> List[str]:
          
          from gnucash_portfolio import BookAggregate
  
          holdings = []
  
          with BookAggregate() as book:
              # query = book.securities.query.filter(Commodity.)
              holding_entities = book.securities.get_all()
              for item in holding_entities:
                  # Check holding balance
                  agg = book.securities.get_aggregate(item)
                  balance = agg.get_num_shares()
                  if balance > Decimal(0):
                      holdings.append(f"{item.namespace}:{item.mnemonic}")
                  else:
                      self.logger.debug(f"0 balance for {item}")
              # holdings = map(lambda x: , holding_entities)
  
          return holdings
docs: Identifies all the securities with positive balances