title: Setting specific values in list of list within csv file
body: <p>what would be the correct way to set certain values of a list of lists to 0 then writing these back to a csv file?</p>
  
  <p>For example:  </p>
  
  <pre><code>list = [[a, 1, 0] , [b, 2, 5], [c, 6, 9], ............]  
  </code></pre>
  
  <p>Required output:  </p>
  
  <pre><code>list = [[a, 0, 0] , [b, 0, 0], [c, 0, 0], ............]  
  </code></pre>