title: When creating the list "Amounts_list" looks like values are not getting added to the list. I get a None value
body: <p>This program should give me the total amount to be paid taking into account all the products that have been introduced by the user. The problem: When creating the list "Amounts_list" looks like values are not getting added to the list.</p>
  
  <p>products_invoice = []</p>
  
  <p>Totals = []</p>
  
  <p>def interaction():</p>
  
  <pre><code>*#selecting first product/quantity*
  
  code = int(input("add article code: "))
  
  price = {1: 5, 2:10, 3:15, 4:20, 5:25, 6:30, 7:35, 8:40, 9:45, 10:50} 
  
  *#article with code 1 costs 5$*
  
  print(f"The price is: {price[code]} $")
  
  quantity = int(input("add quantity: "))
  
  print(f"The total to be paid is: {((price[code])*quantity)} $")
  
  product = code, price[code]*quantity
  
  global products_invoice
  
  products_invoice.append(product)
  print(f"products invoice: {products_invoice}") #to debug
  product_to_list = list(product) *#converting to a list to be able to extract product[1]*
  Amount = product[1]
  print(Amount)
  
  global Totals *#creating a new list to add Amount/product[1] which later on I want to add up*
  Amounts_list = Totals.append(Amount) 
  print(Amounts_list)  **#I get a None instead of printing the list.**
  
  *#adding up the product[1] amounts/costs of all the introduced articles, to get the grand total.*
  Grand_Total = sum(Amounts_list,0)
  print(Grand_Total)
  </code></pre>