title: permanently replace values in a list using Python
body: <pre><code>list1 = [1,2,3,4,5,6,7,8,9]
  def replace():
  
      input_list = input("Enter three numbers separated by commas: ")
      list2 = input_list.split(',')
      list2 = [int(x.strip())for x in list2]
  
      del list1[-3:]
      list1.insert(0,list2)
  
      print(list1)
  </code></pre>
  
  <p>for input 12,13,14
  this gives as a result [[12,13,14],1,2,3,4,5,6]
  Firstly I would like to have a 'flat' list as the result and can't seem to get this right [12,13,14,1,2,3,4,5,6]. I can get the last value entered as part of the list by removing the square brackets from the list2=[int(x.strip()) for...] statement, gives [14,1,2,3,4,5,6].
  My second wish is that I can change the initial list permanently ie [12,13,14,1,2,3,5,6] becomes list1 that is called in the first place. Do I need to save this as a csv file and write to it? I am very new to this, so please forgive me if this is a very simple or stupid batch of questions.</p>