title: How to concat hour with date in python
body: <p>I have a pandas dataframe where date and hour is in two different columns as shown below -
  I want to concat these two columns to have a new datatime column where I can apply pandas window/shift functions. Please share your views.</p>
  
  <pre><code>        date          hour
  0       20190409       0
  1       20190409       0
  2       20190409       0
  3       20190409       0
  4       20190409       0
  </code></pre>