title: Replace one string in a list of strings
body: <p>I have a list of strings.</p>
  
  <p>If one of the strings (e.g. at index 5) is the empty string, I want to replace it with "N". </p>
  
  <p>How do I do that? The naive method (for a java programmer) does not work:</p>
  
  <pre><code>string_list[5] = "N"
  </code></pre>
  
  <p>gives </p>
  
  <blockquote>
    <p>'str' object does not support item assignment</p>
  </blockquote>
  
  <p>(string_list originally came from a .csv-file- that is why it might contain empty strings.)</p>