title: How to determine last row populated for a certain column in xlsxwriter?
body: <p>I want to insert 'A3' in the ws.write method call automatically by determining that 'A3' is the last row with a value in column 'A'.  The method in xlxswriter below sums the values in cell A1 thru A3 and prints the sum in row 4, column A.   How can I insert 'A3' automatically using xlsxriter? </p>
  
  <pre><code>ws.write(4, 0, '=SUM(A1:A3)')  
  </code></pre>