title: Need of using 'r' before path-name while reading a csv file with pandas
body: <p>a newbie here.
  Could someone tell me why do we use an 'r' in some cases before the path name in the following function?:</p>
  
  <pre><code>df = pd.read_csv(r"Path_name")
  </code></pre>
  
  <p>Thanks in advance</p>