title: How to map from csv file to another one in python?
body: <p>I have 2 csv files . The first one looks like this :  </p>
  
  <pre><code>ID , Exersice 
  1 , 1.1
  1 , 1.2
  3 , 1.4
  .
  .
  </code></pre>
  
  <p>it simply contains the IDs of students and exercises they had done .
  the second one contains the IDs and the grade of each one   :</p>
  
  <pre><code>ID , 1.1 , 1.2 ,1.3 ...
  1  , 5   , 9   ,8   ...
  3  , 4   , 10  ,6   ...
  .
  .
  </code></pre>
  
  <p>so how to map from the second file to the first one to be like this   :</p>
  
  <pre><code>ID , Exercise , grade 
  1  , 1.1      , 5
  1  , 1.2      , 9
  .
  .
  </code></pre>