code: def get_dividend_sum_for_symbol(book: Book, symbol: str):
      
      svc = SecuritiesAggregate(book)
      security = svc.get_by_symbol(symbol)
      sec_svc = SecurityAggregate(book, security)
      accounts = sec_svc.get_income_accounts()
      total = Decimal(0)
  
      for account in accounts:
          # get all dividends.
          income = get_dividend_sum(book, account)
          total += income
  
      return total
docs: Calculates all income for a symbol