title: Copy and add the last line of a python pandas data frame on to itself with updated index
body: <p>I have a dataframe such as:</p>
  
  <hr>
  
  <p>2013-07 114.60 89.62 125.64</p>
  
  <p>2013-08 111.55 88.63 121.57</p>
  
  <p>2013-09 108.31 86.24 117.93 </p>
  
  <hr>
  
  <p>index is YY-MM date series I would like to copy and add the last row to the original dataframe with a new updated index. The new dataframe should look like:</p>
  
  <hr>
  
  <p>2013-07 114.60 89.62 125.64 </p>
  
  <p>2013-08 111.55 88.63 121.57</p>
  
  <p>2013-09 108.31 86.24 117.93 </p>
  
  <p>2013-10 108.31 86.24 117.93</p>
  
  <hr>
  
  <p>how can I do this?</p>