title: Invert indices of two lists in Python
body: <p>I need to compare two lists (list1 and list2) on sign changes and I want to invert those indices in the second list that undergo sign changes. This means that I want to change the -4 and the -11 in list2 to 4 and 11. How can I do this?</p>
  <pre><code>list1 = [1,4,5,6,8,10]
  list2 = [3,10,-4,7,-11,10]
  </code></pre>