title: Double Looping in python
body: <p>Please help me with this.</p>
  
  <p>For example, if I have <code>a = [2, 5, 8, 4]</code> and <code>b = [1, 3, 6, 9]</code>.
  how would I used "for" loop to pick an element in 'a' and its corresponding element in 'b' to use in other function? For instance, pick 2 in 'a' and pick 1 in 'b' then next pick 5 in 'a' and 3 in 'b'. </p>