title: Concatenate two numerical values to make a new column using pandas?
body: <p>I have two columns in my dataframe.</p>
  
  <pre><code>var1    var2
  01       001
  </code></pre>
  
  <p>I would like to create a third column that joins them together:</p>
  
  <pre><code>var1    var2    var3
  01       001    01001
  </code></pre>
  
  <p>Does anyone know how to do this? Thank you!</p>