title: Update values of a column which are depending on other column present in the same DataFrame in python
body: <ul>
  <li><em>I am using python in jupyter notebook.</em></li>
  </ul>
  
  <p>A DataFrame(df) is given : </p>
  
  <pre><code>df = pd.DataFrame({'Grade': ['A','B','C','D','E','A','B'],'MArks':['100','','','70','','','']})
  
  
     Grade    MArks
  0   A       100
  1   B   
  2   C   
  3   D       70
  4   E   
  5   A   
  6   B   
  </code></pre>
  
  <p>Given dictionary name(<strong>'scaling'</strong>) is as follows : </p>
  
  <pre><code>scaling = {'A':100,'B':90,'C':80,'D':75,'E':70}
  </code></pre>
  
  <p>How to update column <strong>"MArks"</strong> as per the given '<strong>scaling'</strong>? </p>