title: same input twice not to be entered twice
body: <p>I am making program that builds a shopping list for a user. It should
  repeatedly ask the user for items until they enter 'end' and then it should print the list. If the user has already added an item it should be ignored the next time. I got the problem with the last part where it should ignore the duplicate.I am also required use 'continue' but no idea how to implement to my code.</p>
  
  <pre><code>shoppingListVar = []
  while True:
      item = input("Enter your Item to the List: ")
      shoppingListVar.append(item)
      if item in item:
          print("you already got this item in the list")
      if item == "end":
          break
  print ("The following elements are in your shopping list:")
  print (shoppingListVar)
  </code></pre>